Lubricant base oil and method for producing same

ABSTRACT

A lubricant base oil that is a hydrocarbon oil having a kinematic viscosity at 100° C. of 2.0 to 9 mm 2 /s, a viscosity index of 130 or more, a freezing point of −30 to −5° C., and an SBV viscosity at −20° C. of 1,000 to 60,000 mPa·s, in which the freezing point of the lubricant base oil is higher by 10° C. or more than a freezing point of raffinate obtained by bringing the lubricant base oil into contact with urea and removing paraffin that can be included in the urea.

TECHNICAL FIELD

The present invention relates to a lubricant base oil and a method for producing the same.

BACKGROUND ART

Conventionally, regarding a lubricant base oil and a lubricant oil composition, satisfaction of both a high viscosity index and a low-temperature viscosity characteristic has been attempted.

For example, by blending an additive agent such as a pour-point depressant into a lubricant base oil such as a highly-refined mineral oil, improvement of a low-temperature viscosity characteristic of a lubricant oil has been attempted (for example, refer to Patent Literature 1 to 3). Moreover, as a producing method of a high viscosity index base oil, for feedstock containing natural and synthetic normal paraffins, a method of refining a lubricant base oil by hydrocracking/hydroisomerization is known (for example, refer to Patent Literature 4 to 6).

A pour point is generally as an evaluation index of a low-temperature viscosity characteristic of a lubricant base oil and a lubricant oil. In addition, a technique for evaluating a low-temperature viscosity characteristic based on a lubricant base oil such as the content of normal paraffins and isoparaffins is also known.

CITATION LIST Patent Literature

Patent Literature 1: JP-A-04-036391

Patent Literature 2: JP-A-04-068082

Patent Literature 3: JP-A-04-120193

Patent Literature 4: JP-A-2005-154760

Patent Literature 5: JP-T-2006-502298

Patent Literature 6: JP-T-2002-503754

SUMMARY OF INVENTION Technical Problem

As described above, in general, it is considered that colder flow property of a lubricant base oil is better, and according to the study of the present inventors, a conventional lubricant base oil having cold flow property has a room for improvement in a lubricating property.

The present invention has been made in view of these circumstances, and it is an object of the present invention to provide a lubricant base oil capable of satisfying both a low-temperature viscosity characteristic and a lubricating property at a high level, and a method for producing same.

Solution to Problem

In order to achieve the above-described object, firstly, the present inventors studied the reason why a lubricant base oil having a low pour point is inferior in a lubricating property. As a result, it was found that, in such a lubricant base oil, in addition to normal paraffins, the content of isoparaffins (for example, main chain is long, and branched degree is low) whose structure is similar to that of normal paraffins is also decreased by being highly refined, and thus, a lubricating property tends to be impaired. According to further study based on such a knowledge, it was found that, in a lubricant base oil whose kinematic viscosity at 100° C., viscosity index, freezing point, and SBV viscosity at −20° C. satisfy their respective specific conditions, by making a difference between a freezing point of raffinate obtained by bringing the lubricant base oil into contact with urea and removing paraffin that can be included in the urea and the freezing point of the lubricant base oil be within a specific range, a lubricating property can be improved while maintaining a sufficient low-temperature viscosity characteristic to complete the present invention.

Furthermore, in the present invention, as an approach different from improvement in a low-temperature viscosity characteristic of a lubricant base oil using a pour point as an index, satisfaction of both a low-temperature viscosity characteristic and a lubricating property of a lubricant base oil is attempted using an SBV viscosity as an index. In addition, conventionally, a pour point used as an index of a low-temperature viscosity characteristic of a lubricant base oil evaluates ease of flow, that is to say, a bulk viscosity. In contrast, the SBV viscosity in the present invention can evaluate not a bulk viscosity but mobility of a base oil at the molecular level. For example, a lubricant base oil does not flow at a temperature lower than a pour point, but can move at the molecular level due to distortion between molecules constituting the base oil to impart the SBV viscosity. It was found that, in a lubricant base oil whose kinematic viscosity at 100° C., viscosity index, and freezing point satisfy their respective specific conditions by making the SBV viscosity at −20° C. of the lubricant base oil be 3,000 to 60,000 mPa·s and moreover, by making a difference between a freezing point of raffinate and the freezing point of the lubricant oil be 10° C. or more, both a low-temperature viscosity characteristic and a lubricating property can be satisfied, and furthermore, a sealing property that is likely to become a problem in a lubricant base oil having a low pour point can also be improved. The present invention was made based on the present inventors' own findings as described above.

That is, the present invention provides a lubricant base oil according to the following [1] to [4], and a method for producing a lubricant base oil according to the following [5] to [10].

[1] A lubricant base oil that is a hydrocarbon oil having a kinematic viscosity at 100° C. of 2.0 to 9 mm²/s, a viscosity index of 130 or more, a freezing point of −30 to −5° C., and an SBV viscosity at −20° C. of 1,000 to 60,000 mPa·s, in which

the freezing point of the lubricant base oil is higher by 10° C. or more than a freezing point of raffinate obtained by bringing the lubricant base oil into contact with urea and removing paraffin that can be included in the urea.

[2] The lubricant base oil according to [1], which is a hydrocarbon oil having a kinematic viscosity at 100° C. of 3.0 to 5.0 mm²/s, a viscosity index of 145 or more, a freezing point of −20 to −5° C., and an SBV viscosity at −20° C. of 3,000 to 60,000 mPa·s, in which

the freezing point of the lubricant base oil is higher by 10° C. or more than a freezing point of raffinate obtained by bringing the lubricant base oil into contact with urea and removing paraffin that can be included in the urea.

[3] The lubricant base oil according to [1], which is a hydrocarbon oil having a kinematic viscosity at 100° C. of 5 to 9 mm²/s, a viscosity index of 155 or more, a freezing point of −15 to −5° C., and an SBV viscosity at −20° C. of 3,000 to 30,000 mPa·s, in which

the freezing point of the lubricant base oil is higher by 10° C. or more than a freezing point of raffinate obtained by bringing the lubricant base oil into contact with urea and removing paraffin that can be included in the urea.

[4] The lubricant base oil according to claim 1, which is a hydrocarbon oil having a kinematic viscosity at 100° C. of 2.0 to 3.0 mm²/s, a viscosity index of 130 or more, a freezing point of −30 to −10° C., and an SBV viscosity at −30° C. of 1,000 to 30,000 mPa·s, in which

the freezing point of the lubricant base oil is higher by 15° C. or more than a freezing point of raffmate obtained by bringing the lubricant base oil into contact with urea and removing paraffin that can be included in the urea.

[5] A method for producing a lubricant base oil, the method including

a first step of fractionating, from a hydrocarbon oil containing a base oil fraction and a heavy fraction that is heavier than the base oil fraction, the base oil fraction and the heavy fraction,

a second step of returning a cracked oil obtained by hydrocracking the heavy fraction fractionated in the first step, to the first step,

a third step of obtaining a dewaxed oil by performing hydroisomerization dewaxing of the base oil fraction,

a fourth step of obtaining a refined oil by refining the dewaxed oil, and

a fifth step of obtaining a lubricant base oil that is a hydrocarbon oil having a kinematic viscosity at 100° C. of 2.0 to 9 mm²/s, a viscosity index of 130 or more, a freezing point of −30 to −5° C., and an SBV viscosity at −20° C. of 1,000 to 60,000 mPa·s, by fractionation of the refined oil, in which

the third step is a step of performing hydroisomerization dewaxing of the base oil fraction such that the freezing point of the lubricant base oil obtained in the fifth step is higher by 10° C. or more than a freezing point of raffinate obtained by bringing the lubricant base oil into contact with urea and removing paraffin that can be included in the urea.

[6] The method according to [5], in which

the fifth step is a step of obtaining a lubricant base oil that is a hydrocarbon oil having a kinematic viscosity at 100° C. of 3.0 to 5.0 mm²/s, a viscosity index of 145 or more, a freezing point of −20 to −5° C., and an SBV viscosity at −20° C. of 3,000 to 60,000 mPa·s, by fractionation of the refined oil, and

the third step is a step of performing hydroisomerization dewaxing of the base oil fraction such that the freezing point of the lubricant base oil obtained in the fifth step is higher by 10° C. or more than a freezing point of raffinate obtained by bringing the lubricant base oil into contact with urea and removing paraffin that can be included in the urea.

[7] The method according to claim 5, in which

the fifth step is a step of obtaining a lubricant base oil that is a hydrocarbon oil having a kinematic viscosity at 100° C. of 5 to 9 mm²/s, a viscosity index of 155 or more, a freezing point of −15 to −5° C., and an SBV viscosity at −20° C. of 3,000 to 30,000 mPa·s, by fractionation of the refined oil.

[8] The method according to [5], in which

the fifth step is a step of obtaining a lubricant base oil that is a hydrocarbon oil having a kinematic viscosity at 100° C. of 2.0 to 3.0 mm²/s, a viscosity index of 130 or more, a freezing point of −20 to −5° C., and an SBV viscosity at −30° C. of 1,000 to 30,000 mPa·s, by fractionation of the refined oil, and

the third step is a step of performing hydroisomerization dewaxing of the base oil fraction such that the freezing point of the lubricant base oil obtained in the fifth step is higher by 10° C. or more than a freezing point of raffinate obtained by bringing the lubricant base oil into contact with urea and removing paraffin that can be included in the urea.

[9] The method according to any one of [5] to [8], in which the third step is a step of performing hydroisomerization dewaxing of the base oil fraction in the presence of a hydroisomerization catalyst containing at least one crystalline solid acidic substance selected from the group consisting of ZSM-22-type zeolite, ZSM-23-type zeolite, SSZ32, and ZSM-48-type zeolite, and platinum and/or palladium as an active metal.

[10] The method according to any one of [5] to [9], in which the hydrocarbon oil in the first step is obtained by using GTL wax obtained by a Fischer-Tropsch synthesis or slack wax obtained by solvent dewaxing, as a raw material.

Here, the kinematic viscosity and the viscosity index in the present invention mean a kinematic viscosity and a viscosity index measured in conformity with JIS K 2283-1993, respectively.

Moreover, the SBV viscosity in the present invention means a value measured by a method in which a viscosity is continuously measured by rotating a rotor at 0.3 rpm while cooling at a cooling rate of 1° C./hour, which is a test method defined in ASTM D5133.

In the method for producing a lubricant base oil according to the above-described [5] to [10], the base oil faction and the heavy fraction are fractionated from the hydrocarbon oil as a raw material (first step), and the cracked oil obtained by hydrocracking the heavy fraction is returned to the first step (second step). That is, since only the heavy fraction is offered to the subsequent hydroisomerization dewaxing (third step) after passing through the hydrocracking and the base oil fraction is offered to hydroisomerization dewaxing without passing through the hydrocracking, isomerization of the entire treated oil to be offered to hydroisomerization dewaxing becomes difficult to proceed compared to the conventional method for producing a highly-refined mineral oil. Then, with respect to such a treated oil, hydroisomerization dewaxing is performed such that the difference between freezing points of the lubricant base oil to be finally obtained and raffinate is 10° C. or more, and the obtained dewaxed oil is refined to obtain the refined oil (fourth step), and furthermore, the refined oil is fractionated (fifth step) so that the desired lubricant base oil can be effectively obtained.

In addition, as the conventional method for producing a highly-refined mineral oil, hydrocracking and hydroisomerization dewaxing are generally performed for entire feedstock, but in this case, it becomes difficult to obtain a lubricant base oil in which all of a kinematic viscosity at 100° C., a viscosity index, a freezing point, an SBV viscosity at −20° C., and a difference between freezing points of the lubricant base oil and raffinate satisfy the above-described conditions, and both a low-temperature viscosity characteristic and a lubricating property cannot be satisfied.

In particular, compared to the lubricant base oil according to the above-described [2] and the method for producing a lubricant base oil according to the above-described [6], in the case of the conventional method for producing a highly-refined mineral oil, when the kinematic viscosity at 100° C. is within a range of 3.0 to 5.0 mm²/s, the freezing point tends to be less than −20° C., the SBV viscosity at −20° C. tends to be less than 3,000 mPa·s, and the difference between freezing points of the lubricant oil and raffinate tends to be less than 10° C.

Moreover, compared to the lubricant base oil according to the above-described [3] and the method for producing a lubricant base oil according to the above-described [7], in the case of the conventional method for producing a highly-refined mineral oil, when the kinematic viscosity at 100° C. is within a range of 5 to 9 mm²/s, the freezing point tends to be less than −15° C., the SBV viscosity at −20° C. tends to be less than 3,000 mPa·s, and the difference between freezing points of the lubricant oil and raffinate tends to be less than 10° C.

Moreover, compared to the lubricant base oil according to the above-described [4] and the method for producing a lubricant base oil according to the above-described [8], in the case of the conventional method for producing a highly-refined mineral oil, when the kinematic viscosity at 100° C. is within a range of 2.0 to 3.0 mm²/s, the freezing point tends to be less than −30° C., the SBV viscosity at −30° C. tends to be less than 1,000 mPa·s, and the difference between freezing points of the lubricant oil and raffinate tends to be less than 15° C.

Advantageous Effects of Invention

According to the present invention, a lubricant base oil capable of satisfying both a low-temperature viscosity characteristic and a lubricating property at a high level, and a method for producing same are provided. Furthermore, due to the excellent low-temperature viscosity characteristic and lubricating property, the lubricant base oil of the present invention has an effect of exhibiting an excellent fuel-consumption saving property in JC08 cold mode.

DESCRIPTION OF EMBODIMENTS

Preferred embodiments of the present invention will now be described in more detail.

First Embodiment Lubricant Base Oil

The lubricant base oil according to the first embodiment of the present invention is a lubricant base oil that is a hydrocarbon oil having a kinematic viscosity at 100° C. of 2.0 to 9 mm²/s, a viscosity index of 130 or more, a freezing point of −30 to −5° C., and an SBV viscosity at −20° C. of 1,000 to 60,000 mPa·s, in which the freezing point of the lubricant base oil is higher by 10° C. or more than a freezing point of raffinate obtained by bringing the lubricant base oil into contact with urea and removing paraffin that can be included in the urea.

Examples of the preferred lubricant base oil include the following lubricant base oils A, B, and C.

[Lubricant Base Oil A]

The lubricant base oil A is a lubricant base oil that is a hydrocarbon oil having a kinematic viscosity at 100° C. of 3.0 to 5.0 mm²/s, a viscosity index of 145 or more, a freezing point of −20 to −5° C., and an SBV viscosity at −20° C. of 3,000 to 60,000 mPa·s, in which the freezing point of the lubricant base oil is higher by 10° C. or more than a freezing point of raffinate obtained by bringing the lubricant base oil into contact with urea and removing paraffin that can be included in the urea.

The kinematic viscosity of the lubricant base oil A at 100° C. is 3.0 to 5.0 mm²/s, preferably 3.2 to 4.3 mm²/s, and more preferably 3.4 to 4.1 mm²/s.

Moreover, the kinematic viscosity of the lubricant base oil A at 40° C. is preferably 10 to 20 mm²/s, and more preferably 12 to 16 mm²/s.

Moreover, the viscosity index of the lubricant base oil A is 145 or more, preferably 147 or more, and more preferably 148 to 160. In addition, if the viscosity index is less than the above-described lower limit, an energy saving property is decreased, and if it exceeds the above-described upper limit, fluidity at ordinary temperature is decreased and the lubricant base oil A tends to be not able to be used as a lubricant base oil.

Moreover, the freezing point of the lubricant base oil A is −20 to −5° C., preferably −18 to −8° C., and more preferably −15 to −10° C. In addition, if the freezing point is less than the above-described lower limit, an energy saving property is decreased, and if it exceeds the above-described upper limit, fluidity at ordinary temperature is decreased and the lubricant base oil A cannot be used as a lubricant base oil.

Moreover, the SBV viscosity of the lubricant base oil A at −20° C. is 3,000 to 60,000 mPa·s, preferably 3,000 to 30,000 mPa·s, and more preferably 3,000 to 15,000 mPa·s. If the SBV viscosity at −20° C. is less than the above-described lower limit, a sealing property is insufficient, and if it exceeds the above-described upper limit, a low temperature temperature characteristic is insufficient.

Moreover, the SBV viscosity of the lubricant base oil A at −30° C. is preferably 50,000 to 500,000 mPa·s, more preferably 50,000 to 400,000 mPa·s, and further preferably 50,000 to 300,000 mPa·s. If the SBV viscosity at −25° C. is less than the above-described lower limit, a sealing property tends to be insufficient, and if it exceeds the above-described upper limit, a low temperature temperature characteristic tends to be insufficient.

Moreover, the freezing point of the lubricant base oil A is higher by 10° C. or more, preferably 10 to 12° C., and more preferably 10 to 14° C. than a freezing point of raffinate obtained by bringing the lubricant base oil into contact with urea and removing paraffin that can be included in the urea. If the difference between the freezing points is less than the above-described lower limit, a lubricating property is insufficient, and if it exceeds the above-described upper limit, fluidity as a base oil is decreased, and the lubricant base oil tends to be difficult to be used as a base oil.

Examples of a procedure for obtaining raffinate by bringing the lubricant base oil into contact with urea and removing paraffin that can be included in the urea include the following procedure.

In a round-bottom flask, 100 g of a weighed sample oil (lubricant base oil) is charged, and 200 g of urea, 360 ml of toluene, and 40 ml of methanol are added to be stirred at room temperature for 6 hours. Accordingly, a white granular crystal is generated as a urea adduct in the reaction liquid. The reaction liquid is filtered by a 1 micron filter to collect the generated white granular crystal, and the obtained crystal is washed with 50 ml of toluene 6 times. The collected white crystal is charged in a flask, and 300 ml of pure water and 300 ml of toluene are added to be stirred at 80° C. for 1 hour. A water phase is separation-removed with a separating funnel, and a toluene phase is washed with 300 ml of pure water 3 times. A dewatering process is performed by adding a drying agent (sodium sulfate) to the toluene phase, and then, toluene is distilled away. A rate (mass percentage) of the urea adduct obtained in this manner to the sample oil is defined as “urea adduct value”.

Furthermore, in the case of performing a ¹³C-NMR analysis of the lubricant base oil A, a rate of CH₂ carbons constituting the main chain to all carbons constituting the lubricant base oil is preferably 15% or more, and more preferably 16% or more. If the rate is the above-described lower limit or more, a traction coefficient of the lubricant base oil can be decreased (that is, low friction), and it is preferable in terms of an energy saving property. In addition, the rate of CH₂ carbons constituting the main chain can be determined, for example, by performing the ¹³C-NMR analysis under the following analysis conditions.

The rate of CH₂ to the total amount of the constituent carbons of the lubricant base oil means a rate of the total of integral intensity attributed to the CH, main chain with respect to the total of integral intensity of all carbons, which are measured by ¹³C-NMR, and other methods may be used as long as the equivalent result is obtained. In addition, in the present invention, in the ¹³C-NMR measurement, a diluted sample obtained by adding 3 g of deuterated chloroform to 0.5 g of a sample was used, the measurement temperature was room temperature, and the resonant frequency was 100 MHz. In addition, a gated coupling method was used as the measurement method.

Furthermore, in the case of performing an FD-MS analysis of the lubricant base oil A, a cycloparaffin content is preferably 50% or less, and more preferably 40% or less. If the cycloparaffin content is the above-described upper limit or less, abrasion resistance of the lubricant base oil can be further improved. In addition, the rate of the cycloparaffin content can be determined, for example, by performing the FD-MS analysis under the following analysis conditions.

The FD method is an ionization method in which a sample is coated on an emitter, a current is applied to the emitter to heat the coated sample, and a tunneling effect is used in a high electrical field on the emitter surface and in the vicinity of the whisker tip. In the present invention, the measurement was performed using JMS-AX505H by JEOL Ltd. under conditions of an accelerating voltage (cathode voltage) of 3.0 kV and an emitter current of 2 mA/min. Compound types in mass spectrometry are determined by specific ions to be formed, and they are generally classified by a z value. The z value is represented by a general formula C_(n)H_(2n+z) for all hydrocarbon species. Since the saturated phase is analyzed separately from the aromatic phase, contents of different cycloparaffins having the same stoichiometry can be measured. In addition, cycloparaffins include both of monocyclic cycloparaffins and bicyclic or more cycloparaffins.

Moreover, from the viewpoint of improving a low-temperature viscosity characteristic without impairing a viscosity-temperature characteristic at high temperature, the urea adduct value of the lubricant base oil A is preferably 4% by mass or less, more preferably 3.5% by mass or less, further preferably 3% by mass or less, and particularly preferably 2.5% by mass or less. Furthermore, the urea adduct value of the lubricant base oil may be 0% by mass. However, since a sufficient low-temperature viscosity characteristic and a lubricant base oil having a higher viscosity index can be obtained, and furthermore, dewaxing conditions are loosened to result in excellent economic efficiency, it is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and particularly preferably 0.8% by mass or more.

Moreover, the content of the saturated content in the lubricant base oil A is, on the basis of the total amount of the lubricant base oil, preferably 90% by mass or more, more preferably 93% by mass or more, further preferably 95% by mass or more, and particularly preferably 99% by mass or more. The content of the saturated content satisfies the above-described condition so that a viscosity-temperature characteristic and thermal-oxidation stability can be achieved, and furthermore, in the case where an additive agent is blended into the lubricant base oil, the additive agent is sufficiently stably dissolved and maintained in the lubricant base oil and functions of the additive agent can be expressed at a high level. Furthermore, a friction characteristic of the lubricant base oil itself can be improved, and as a result, improvement in a friction-reducing effect and therefore improvement in an energy saving property can be achieved. In addition, the content of the saturated content in the present invention means a value (unit: % by mass) measured in conformity with ASTM D 2007-93.

Moreover, the aromatic content in the lubricant base oil A is, on the basis of the total amount of the lubricant base oil, preferably 5% by mass or less, more preferably 0.05 to 3% by mass, further preferably 0.1 to 1% by mass, and particularly preferably 0.1 to 0.5% by mass. If the content of the aromatic content exceeds the above-described upper limit, a viscosity-temperature characteristic, thermal-oxidation stability, a friction characteristic, and furthermore, a volatilization-preventing property, and a low-temperature viscosity characteristic tend to be decreased, and moreover, in the case where an additive agent is blended into the lubricant base oil, an effect of the additive agent tends to be decreased. Furthermore, although the lubricant base oil according to the present embodiment may not contain the aromatic content, solubility of the additive agent can be further increased by making the content of the aromatic content be 0.05% by mass or more.

In addition, the content of the aromatic content in the present invention means a value measured in conformity with ASTM D 2007-93. Generally, the aromatic content includes, in addition to alkylbenzenes and alkylnaphthalenes, anthracene, phenanthrene, alkylated products thereof, and moreover, compounds in which four benzene rings or more are condensed, and aromatic compounds having a hetero atom, such as pyridines, quinolines, phenols, and naphthols.

Furthermore, the content of the sulfur content in the lubricant base oil A depends on the content of the sulfur content in the raw material. For example, in the case of using a raw material substantially not containing sulfur, such as a synthetic wax constituent obtained by a Fischer-Tropsch reaction or the like, a lubricant base oil substantially not containing sulfur can be obtained. Moreover, in the case of using a raw material containing sulfur, such as slack wax obtained in the refining process of the lubricant base oil and micro wax obtained in the wax refining process, the sulfur content in the obtained lubricant base oil is generally 100 mass ppm or more. In the lubricant base oil of the present invention, in terms of further improvement in thermal-oxidation stability and reduction in the sulfur content, the content of the sulfur content is preferably 10 mass ppm or less, more preferably 5 mass ppm or less, further preferably 3 mass ppm or less, and particularly preferably 1 mass ppm or less.

Furthermore, in terms of cost reduction, slack wax or the like is preferably used as a raw material, and in this case, the sulfur content in the obtained lubricant base oil is preferably 50 mass ppm or less, and more preferably 10 mass ppm or less. In addition, the sulfur content in the present invention means a sulfur content measured in conformity with JIS K 2541-1996.

Moreover, the pour point of the lubricant base oil A is preferably −5° C. or less, more preferably −12.5° C. or less, and further preferably −12.5° C. or less. If the pour point exceeds the above-described upper limit, cold flow property of the entire lubricant oil using the lubricant base oil tends to be decreased. Furthermore, the pour point of the lubricant base oil according to the present embodiment is preferably −20° C. or more, more preferably −17.5° C. or more, and further preferably −15° C. or more. If the pour point is less than −20° C., it becomes difficult for the SBV viscosity at −20° C. to be within a range of 3,000 to 60,000 mPa·s, and a sealing property tends to be insufficient. In addition, the pour point in the present invention means a pour point measured in conformity with JIS K 2269-1987.

Moreover, the CCS viscosity of the lubricant base oil A at −30° C. is preferably 1,500 mPa·s or less, and more preferably 1,200 mPa·s or less. Furthermore, the CCS viscosity of the lubricant base oil at −35° C. is preferably 2,500 mPa·s or less, and more preferably 2,000 mPa·s or less. If the CCS viscosity at −30° C. or at −35° C. exceeds the above-described upper limit, cold flow property of the entire lubricant oil using the lubricant base oil tends to be decreased. In addition, the CCS viscosity at −30° C. or at −35° C. means a viscosity measured in conformity with JIS K 2010-1993.

Moreover, the density of the lubricant base oil A at 15° C. (ρ₁₅) is preferably a ρ value represented by the following formula (1) or less, that is ρ₁₅≦ρ.

ρ=0.0025×kv100+0.816  (1)

[In the formula, kv100 represents kinematic viscosity of lubricant base oil at 100° C. (mm²/s).]

In addition, in the case of ρ₁₅>ρ, a viscosity-temperature characteristic, thermal-oxidation stability, and furthermore, a volatilization-preventing property, and a low-temperature viscosity characteristic tend to be decreased, and moreover, in the case where an additive agent is blended into the lubricant base oil, an effect of the additive agent tends to be decreased.

More specifically, ρ₁₅ of the lubricant base oil is preferably 0.815 or less, and more preferably 0.810 or less.

In addition, the density at 15° C. in the present invention means a density measured at 15° C. in conformity with JIS K 2249-1995.

Moreover, the NOACK evaporation of the lubricant base oil A is preferably 8% by mass or more, more preferably 9% by mass or more, further preferably 10 or more, and moreover, preferably 15% by mass or less, more preferably 14% by mass or less, and further preferably 13% by mass or less. When the NOACK evaporation is the above-described lower limit, improvement in a low-temperature viscosity characteristic tends to become difficult. Furthermore, the NOACK evaporation exceeding the above-described upper limit is not preferable because, in the case where the lubricant base oil is used for an internal combustion engine lubricant oil or the like, evaporation loss of the lubricant oil is increased, and therefore, catalyst poisoning is accelerated. In addition, the NOACK evaporation in the present invention means evaporation loss measured in conformity with ASTM D 5800-95.

[Lubricant Base Oil B]

The lubricant base oil B is a lubricant base oil that is a hydrocarbon oil having a kinematic viscosity at 100° C. of 3M to 5.0 mm²/s, a viscosity index of 145 or more, a freezing point of −15 to −5° C., and an SBV viscosity at −20° C. of 3,000 to 30,000 mPa·s, in which the freezing point of the lubricant oil is higher by 10° C. or more than a freezing point of raffinate obtained by bringing the lubricant base oil into contact with urea and removing paraffin that can be included in the urea.

The kinematic viscosity of the lubricant base oil B at 100° C. is 5 to 9 mm²/s, preferably 5.5 to 8.5 mm²/s, and more preferably 6 to 8 mm²/s.

Moreover, the kinematic viscosity of the lubricant base oil B at 40° C. is preferably 25 to 40 mm²/s, and more preferably 28 to 35 mm²/s.

Moreover, the viscosity index of the lubricant base oil B is 155 or more, preferably 157 or more, and more preferably 158 to 165. In addition, if the viscosity index is less than the above-described lower limit, an energy saving property is decreased, and if it exceeds the above-described upper limit, fluidity at ordinary temperature is decreased and the lubricant base oil B cannot be used as a lubricant base oil.

Moreover, the freezing point of the lubricant base oil B is −15 to −5° C., preferably −14 to −7° C., and more preferably −13 to −8° C. If the freezing point is less than the above-described lower limit, an energy saving property is decreased, and if it exceeds the above-described upper limit, fluidity at ordinary temperature is decreased and the lubricant base oil B cannot be used as a lubricant base oil.

Moreover, the SBV viscosity of the lubricant base oil B at −20° C. is 3,000 to 30,000 mPa·s, preferably 3,000 to 25,000 mPa·s, and more preferably 3,000 to 20,000 mPa·s. If the SBV viscosity at −20° C. is less than the above-described lower limit, a sealing property is insufficient, and if it exceeds the above-described upper limit, a low temperature temperature characteristic is insufficient.

Moreover, the SBV viscosity of the lubricant base oil B at −25° C. is preferably 5,000 to 500,000 mPa·s, more preferably 5,000 to 400,000 mPa·s, and further preferably 5,000 to 300,000 mPa·s. If the SBV viscosity at −25° C. is less than the above-described lower limit, a sealing property tends to be insufficient, and if it exceeds the above-described upper limit, a low temperature temperature characteristic tends to be insufficient.

Moreover, the freezing point of the lubricant base oil B is higher by 10° C. or more, preferably 10 to 20° C., and more preferably 10 to 15° C. than a freezing point of raffinate obtained by bringing the lubricant base oil into contact with urea and removing paraffin that can be included in the urea. If the difference between the freezing points is less than the above-described lower limit, a lubricating property is insufficient, and if it exceeds the above-described upper limit, fluidity as a base oil is decreased, and the lubricant base oil tends to be difficult to be used as a base oil.

Furthermore, in the case of performing a ¹³C-NMR analysis of the lubricant base oil B, a rate of CH₂ carbons constituting the main chain to all carbons constituting the lubricant base oil is preferably 20% or more, and more preferably 20% or more. If the rate is the above-described lower limit or more, a traction coefficient of the lubricant base oil can be decreased (that is, low friction), and it is preferable in terms of an energy saving property.

Furthermore, in the case of performing an FD-MS analysis of the lubricant base oil B, a cycloparaffin content is preferably 60% or less, and more preferably 65% or less. If the cycloparaffin content is the above-described upper limit or less, abrasion resistance of the lubricant base oil can be further improved.

Moreover, from the viewpoint of improving a low-temperature viscosity characteristic without impairing a viscosity-temperature characteristic at high temperature, the urea adduct value of the lubricant base oil B is preferably 4% by mass or less, more preferably 3.5% by mass or less, further preferably 3% by mass or less, and particularly preferably 2.5% by mass or less. Furthermore, the urea adduct value of the lubricant base oil may be 0% by mass. However, since a sufficient low-temperature viscosity characteristic and a lubricant base oil having a higher viscosity index can be obtained, and furthermore, dewaxing conditions are loosened to result in excellent economic efficiency, it is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and particularly preferably 0.8% by mass or more.

Moreover, the content of the saturated content in the lubricant base oil B is, on the basis of the total amount of the lubricant base oil, preferably 90% by mass or more, more preferably 93% by mass or more, further preferably 95% by mass or more, and particularly preferably 99% by mass or more. The content of the saturated content satisfies the above-described condition so that a viscosity-temperature characteristic and thermal-oxidation stability can be achieved, and furthermore, in the case where an additive agent is blended into the lubricant base oil, the additive agent is sufficiently stably dissolved and maintained in the lubricant base oil and functions of the additive agent can be expressed at a high level. Furthermore, a friction characteristic of the lubricant base oil itself can be improved, and as a result, improvement in a friction-reducing effect and therefore improvement in an energy saving property can be achieved.

Moreover, the aromatic content in the lubricant base oil B is, on the basis of the total amount of the lubricant base oil, preferably 5% by mass or less, more preferably 0.05 to 3% by mass, further preferably 0.1 to 1% by mass, and particularly preferably 0.1 to 0.5% by mass. If the content of the aromatic content exceeds the above-described upper limit, a viscosity-temperature characteristic, thermal-oxidation stability, a friction characteristic, and furthermore, a volatilization-preventing property, and a low-temperature viscosity characteristic tend to be decreased, and moreover, in the case where an additive agent is blended into the lubricant base oil, an effect of the additive agent tends to be decreased. Furthermore, although the lubricant base oil B may not contain the aromatic content, solubility of the additive agent can be further increased by making the content of the aromatic content be 0.05% by mass or more.

Furthermore, the content of the sulfur content in the lubricant base oil B depends on the content of the sulfur content in the raw material. For example, in the case of using a raw material substantially not containing sulfur, such as a synthetic wax constituent obtained by a Fischer-Tropsch reaction or the like, a lubricant base oil substantially not containing sulfur can be obtained. Moreover, in the case of using a raw material containing sulfur, such as slack wax obtained in the refining process of the lubricant base oil and micro wax obtained in the wax refining process, the sulfur content in the obtained lubricant base oil is generally 100 mass ppm or more. In the lubricant base oil of the present invention, in terms of further improvement in thermal-oxidation stability and reduction in the sulfur content, the content of the sulfur content is preferably 10 mass ppm or less, more preferably 5 mass ppm or less, further preferably 3 mass ppm or less, and particularly preferably 1 mass ppm or less.

Furthermore, in terms of cost reduction, slack wax or the like is preferably used as a raw material, and in this case, the sulfur content in the obtained lubricant base oil is preferably 50 mass ppm or less, and more preferably 10 mass ppm or less. In addition, the sulfur content in the present invention means a sulfur content measured in conformity with JIS K 2541-1996.

Moreover, the pour point of the lubricant base oil B is preferably −5° C. or less, more preferably −10° C. or less, and further preferably −12.5° C. or less. If the pour point exceeds the above-described upper limit, cold flow property of the entire lubricant oil using the lubricant base oil tends to be decreased. Furthermore, the pour point of the lubricant base oil B is preferably −20° C. or more, more preferably −17.5° C. or more, and further preferably −15° C. or more. If the pour point is less than −20° C., it becomes difficult for the SBV viscosity at −20° C. to be within a range of 3,000 to 60,000 mPa·s, and a sealing property tends to be insufficient.

Moreover, the CCS viscosity of the lubricant base oil B at −30° C. is preferably 950 mPa·s or less, and more preferably 900 mPa·s or less. Furthermore, the CCS viscosity of the lubricant base oil at −35° C. is preferably 1,600 in Pa·s or less, and more preferably 1,500 mPa·s or less. If the CCS viscosity at −30° C. or at −35° C. exceeds the above-described upper limit, cold flow property of the entire lubricant oil using the lubricant base oil tends to be decreased.

Moreover, the density of the lubricant base oil B at 15° C. (ρ₁₅) is preferably a ρ value represented by the following formula (1) or less, that is ρ₁₅≦ρ.

ρ=0.0025×kv100+0.816  (1)

[In the formula, kv100 represents kinematic viscosity of lubricant base oil at 100° C. (mm²/s).]

In addition, in the case of ρ₁₅>ρ, a viscosity-temperature characteristic, thermal-oxidation stability, and furthermore, a volatilization-preventing property, and a low-temperature viscosity characteristic tend to be decreased, and moreover, in the case where an additive agent is blended into the lubricant base oil, an effect of the additive agent tends to be decreased.

More specifically, ρ₁₅ of the lubricant base oil is preferably 0.830 or less, and more preferably 0.825 or less.

In addition, the density at 15° C. in the present invention means a density measured at 15° C. in conformity with JIS K 2249-1995.

[Lubricant Base Oil C]

The lubricant base oil C is a lubricant base oil that is a hydrocarbon oil having a kinematic viscosity at 100° C. of 2.0 to 3.0 mm²/s, a viscosity index of 130 or more, a freezing point of −30 to −10° C., and an SBV viscosity at −30° C. of 1,000 to 30,000 mP·s or less, in which the freezing point of the lubricant base oil is higher by 15° C. or more than a freezing point of raffinate obtained by bringing the lubricant base oil into contact with urea and removing paraffin that can be included in the urea.

The kinematic viscosity of the lubricant base oil C at 100° C. is 2.0 to 3.0 mm²/s, preferably 2.1 to 2.9 mm²/s, and more preferably 2.2 to 2.8 mm²/s.

Moreover, the kinematic viscosity of the lubricant base oil C at 40° C. is preferably 7 to 12 mm²/s, and more preferably 8 to 10 mm²/s.

Moreover, the viscosity index of the lubricant base oil C is 130 or more, preferably 131 or more, and more preferably 132 to 140. If the viscosity index is less than the above-described lower limit, an energy saving property is decreased, and if it exceeds the above-described upper limit, fluidity at ordinary temperature is decreased and the lubricant base oil C cannot be used as a lubricant base oil.

Moreover, the freezing point of the lubricant base oil C is −30 to −10° C., preferably −29 to −15° C., and more preferably −28 to −20° C. If the freezing point is less than the above-described lower limit, an energy saving property is decreased, and if it exceeds the above-described upper limit, fluidity at ordinary temperature is decreased and the lubricant base oil C cannot be used as a lubricant base oil.

Moreover, the SBV viscosity of the lubricant base oil C at −30° C. is 1,000 to 30,000 mPa·s, preferably 1,000 to 20,000 mPa·s, and more preferably 1,000 to 15,000 mPa·s. If the SBV viscosity at −30° C. is less than the above-described lower limit, a sealing property is insufficient, and if it exceeds the above-described upper limit, a low temperature characteristic is insufficient.

Moreover, the SBV viscosity of the lubricant base oil C at −35° C. is preferably 3,000 to 500,000 mPa·s, more preferably 3,000 to 400,000 mPa·s, and further preferably 3,000 to 300,000 mPa·s. If the SBV viscosity at −35° C. is less than the above-described lower limit, a sealing property is insufficient, and if it exceeds the above-described upper limit, a low-temperature viscosity characteristic is insufficient.

Moreover, the SBV viscosity of the lubricant base oil C at −40° C. is preferably 5,000 to 750,000 mPa·s, more preferably 5,000 to 500,000 mPa·s, and further preferably 5,000 to 400,000 mPa·s. If the SBV viscosity at −40° C. is less than the above-described lower limit, a sealing property is insufficient, and if it exceeds the above-described upper limit, a low-temperature viscosity characteristic is insufficient.

Moreover, a value obtained by dividing a freezing point of raffinate, which is obtained by bringing the lubricant base oil C into contact with urea and removing paraffin that can be included in the urea, by the freezing point of the lubricant base oil is 10° C. or more, preferably 12 to 20° C., and more preferably 15 to 19° C. If the difference between the freezing points is less than the above-described lower limit, a lubricating property is insufficient, and if it exceeds the above-described upper limit, fluidity as a base oil is decreased, and the lubricant base oil tends to be difficult to be used as a base oil.

Furthermore, in the case of performing a ¹³C-NMR analysis of the lubricant base oil C, a rate of CH₂ carbons constituting the main chain to all carbons constituting the lubricant base oil is preferably 15% or more, and more preferably 15% or more. If the rate is the above-described lower limit or more, a traction coefficient of the lubricant base oil can be decreased (that is, low friction), and it is preferable in terms of an energy saving property.

Furthermore, in the case of performing an FD-MS analysis of the lubricant base oil C, a cycloparaffin content is preferably 30% or less, and more preferably 25% or less. If the cycloparaffin content is the above-described upper limit or less, abrasion resistance of the lubricant base oil can be further improved.

Moreover, from the viewpoint of improving a low-temperature viscosity characteristic without impairing a viscosity-temperature characteristic at high temperature, the urea adduct value of the lubricant base oil C is preferably 4% by mass or less, more preferably 3.5% by mass or less, further preferably 3% by mass or less, and particularly preferably 2.5% by mass or less. Furthermore, the urea adduct value of the lubricant base oil may be 0% by mass. However, since a sufficient low-temperature viscosity characteristic and a lubricant base oil having a higher viscosity index can be obtained, and furthermore, dewaxing conditions are loosened to result in excellent economic efficiency, it is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and particularly preferably 0.8% by mass or more.

Moreover, the content of the saturated content in the lubricant base oil C is, on the basis of the total amount of the lubricant base oil, preferably 90% by mass or more, more preferably 93% by mass or more, further preferably 95% by mass or more, and particularly preferably 99% by mass or more. The content of the saturated content satisfies the above-described condition so that a viscosity-temperature characteristic and thermal-oxidation stability can be achieved, and furthermore, in the case where an additive agent is blended into the lubricant base oil, the additive agent is sufficiently stably dissolved and maintained in the lubricant base oil and functions of the additive agent can be expressed at a high level. Furthermore, a friction characteristic of the lubricant base oil itself can be improved, and as a result, improvement in a friction-reducing effect and therefore improvement in an energy saving property can be achieved.

Moreover, the aromatic content in the lubricant base oil C is, on the basis of the total amount of the lubricant base oil, preferably 5% by mass or less, more preferably 0.05 to 3% by mass, further preferably 0.1 to 1% by mass, and particularly preferably 0.1 to 0.5% by mass. If the content of the aromatic content exceeds the above-described upper limit, a viscosity-temperature characteristic, thermal-oxidation stability, a friction characteristic, and furthermore, a volatilization-preventing property, and a low-temperature viscosity characteristic tend to be decreased, and moreover, in the case where an additive agent is blended into the lubricant base oil, an effect of the additive agent tends to be decreased. Furthermore, although the lubricant base oil C may not contain the aromatic content, solubility of the additive agent can be further increased by making the content of the aromatic content be 0.05% by mass or more.

Furthermore, the content of the sulfur content in the lubricant base oil C depends on the content of the sulfur content in the raw material. For example, in the case of using a raw material substantially not containing sulfur, such as a synthetic wax constituent obtained by a Fischer-Tropsch reaction or the like, a lubricant base oil substantially not containing sulfur can be obtained. Moreover, in the case of using a raw material containing sulfur, such as slack wax obtained in the refining process of the lubricant base oil and micro wax obtained in the wax refining process, the sulfur content in the obtained lubricant base oil is generally 100 mass ppm or more. In the lubricant base oil of the present invention, in terms of further improvement in thermal-oxidation stability and reduction in the sulfur content, the content of the sulfur content is preferably 10 mass ppm or less, more preferably 5 mass ppm or less, further preferably 3 mass ppm or less, and particularly preferably 1 mass ppm or less.

Furthermore, in terms of cost reduction, slack wax or the like is preferably used as a raw material, and in this case, the sulfur content in the obtained lubricant base oil is preferably 50 mass ppm or less, and more preferably 10 mass ppm or less. In addition, the sulfur content in the present invention means a sulfur content measured in conformity with JIS K 2541-1996.

Moreover, the pour point of the lubricant base oil C is preferably −5° C. or less, more preferably −12.5° C. or less, and further preferably −15° C. or less. If the pour point exceeds the above-described upper limit, cold flow property of the entire lubricant oil using the lubricant base oil tends to be decreased. Furthermore, the pour point of the lubricant base oil C is preferably −27.5° C. or more, and more preferably −25° C. or more. If the pour point is less than −27.5, it becomes difficult for the SBV viscosity at −20° C. to be within a range of 3,000 to 60,000 mPa·s, and a sealing property tends to be insufficient.

Moreover, the CCS viscosity of the lubricant base oil C at −30° C. is preferably 1,000 mPa·s or less, and more preferably 750 mPa·s or less. Furthermore, the CCS viscosity of the lubricant base oil at −35° C. is preferably 1,300 mPa·s or less, and more preferably 1,000 mPa·s or less. If the CCS viscosity at −30° C. or at −35° C. exceeds the above-described upper limit, cold flow property of the entire lubricant oil using the lubricant base oil tends to be decreased.

Moreover, the density of the lubricant base oil C at 15° C. (ρ₁₅) is preferably a ρ value represented by the following formula (1) or less, that is ρ₁₅≦ρ.

ρ=0.0025×kv100+0.816  (1)

[In the formula, kv100 represents kinematic viscosity of lubricant base oil at 100° C. (mm²/s).]

In addition, in the case of ρ₁₅>ρ, a viscosity-temperature characteristic, thermal-oxidation stability, and furthermore, a volatilization-preventing property, and a low-temperature viscosity characteristic tend to be decreased, and moreover, in the case where an additive agent is blended into the lubricant base oil, an effect of the additive agent tends to be decreased.

More specifically, ρ₁₅ of the lubricant base oil is preferably 0.806 or less, and more preferably 0.8058 or less.

Moreover, the NOACK evaporation of the lubricant base oil C is preferably 20% by mass or more, more preferably 25% by mass or more, further preferably 30 or more, and moreover, preferably 50% by mass or less, more preferably 48% by mass or less, and further preferably 46% by mass or less. When the NOACK evaporation is the above-described lower limit, improvement in a low-temperature viscosity characteristic tends to become difficult. Furthermore, the NOACK evaporation exceeding the above-described upper limit is not preferable because, in the case where the lubricant base oil is used for an internal combustion engine lubricant oil or the like, evaporation loss of the lubricant oil is increased, and therefore, catalyst poisoning is accelerated.

The lubricant base oil according to the present embodiment (including the above-described lubricant base oils A, B, and C) excels in a low-temperature viscosity characteristic and a lubricating property, and can be suitably used as a lubricant base oil for various applications. Specifically, examples of the applications of the lubricant base oil according to the present embodiment include lubricant oils used for internal combustion engines such as passenger vehicle gasoline engines, two-wheel vehicle gasoline engines, diesel engines, gas engines, gas heat pump engines, marine engines, and power-generating engines (internal combustion engine lubricant oil), lubricant oils used for driving transmission devices such as automatic transmissions, manual transmissions, non-stage transmissions, and final reduction gears (driving transmission device oil), hydraulic oils used for hydraulic systems such as dampers and construction machines, compressor oils, turbine oils, industrial gear oils, refrigerant oils, rust preventing oils, heating medium oils, gas holder seal oils, bearing oils, paper machine oils, machine tool oils, sliding guide surface oils, electrical insulating oils, cutting oils, press oils, rolling oils, and heat treating oils, and by using the lubricant base oil according to the present embodiment for these applications, both a low-temperature viscosity characteristic and a lubricating property can be satisfied at a high level.

In the above-described applications, the lubricant base oil according to the present embodiment may be used alone, or the lubricant base oil according to the present embodiment may be used in combination with one, or two or more other base oils. In addition, when the lubricant base oil according to the present embodiment is used in combination with other base oils, a rate of the lubricant base oil of the present invention in the mixed-base oil is preferably 30% by mass or more, more preferably 50% by mass or more, and further preferably 70% by mass or more.

Other base oils used in combination with the lubricant base oil according to the present embodiment are not particularly limited, and examples of mineral base oils include solvent refined mineral oils, hydrocracked mineral oils, hydrorefined mineral oils, and solvent dewaxed base oils having a kinematic viscosity at 100° C. of 1 to 100 mm²/s, for example.

Moreover, examples of synthetic base oils include poly-α-olefins or hydrides thereof, isobutene oligomers or hydrides thereof, isoparaffins, alkylbenzenes, alkylnaphthalenes, diesters (ditridecyl glutarate, di-2-ethylhexyl adipate, diisodecyl adipate, ditridecyl adipate, di-2-ethylhexyl sebacate and the like), polyol esters (trimethylolpropane caprylate, trimethylolpropane pelargonate, pentaerythritol 2-ethylhexanoate, pentaerythritol pelargonate and the like), polyoxyalkylene glycols, dialkyldiphenyl ethers, and polyphenyl ethers, and among them, poly-α-olefins are preferable. Typically, examples of the poly-α-olefins include α-olefin oligomers or co-oligomers having a carbon number of 2 to 32, and preferably 6 to 16 (1-octene oligomer, decene oligomer, ethylene-propylene co-oligomer and the like) and hydrides thereof.

Although a producing method of poly-α-olefins is not particularly limited, examples thereof include a method in which α-olefin is polymerized in the presence of a polymerization catalyst such as a Friedel-Crafts catalyst including a complex of aluminum trichloride or boron trifluoride with water, an alcohol (ethanol, propanol, butanol and the like), a carboxylic acid, or ester.

Furthermore, various additive agents may be blended into the lubricant base oil according to the present embodiment or the mixed-base oil of the lubricant base oil and other lubricant base oils, if necessary. Such additive agents are not particularly limited, and arbitrary additive agents that are conventionally used in the field of lubricant oils can be blended. Specifically, examples of the lubricant oil additive agents include antioxidants, ashless dispersants, detergents, extreme pressure agents, antiwear agents, viscosity index improvers, pour-point depressants, friction modifiers, oiliness agents, corrosion inhibitors, rust-preventive agents, demulsifying agents, metal deactivating agents, seal swelling agents, antifoaming agents, and coloring agents. These additive agents may be used singly or two or more kinds thereof may be used in combination.

For example, the lubricant base oil according to the present embodiment can effectively exhibit the addition effect of a pour-point depressant. Therefore, when the lubricant base oil according to the present embodiment or the mixed-base oil of the lubricant base oil and other lubricant base oils contains a pour-point depressant, an excellent low-temperature viscosity characteristic (MRV viscosity at −40° C. is preferably 20,000 mPa·s or less, more preferably 15,000 mPa·s or less, and further preferably 10,000 mPa·s or less) can be achieved. In addition, the MRV viscosity at −40° C. described herein means an MRV viscosity at −40° C. measured in conformity with JPI-5S-42-93. For example, when a pour-point depressant is blended into the above-described base oils (II) and (V), the MRV viscosity at −40° C. can be 12,000 mPa·s or less, and a lubricant oil composition having an extremely excellent low-temperature viscosity characteristic of more preferably 10,000 mPa·s or less, further preferably 8,000 mPa·s, and particularly preferably 6,500 mPa·s or less can be obtained. In this case, the amount of the pour-point depressant blended is, on the basis of the total amount of the composition, 0.05 to 2% by mass, and preferably 0.1 to 1.5% by mass, in particular, in terms of capable of decreasing the MRV viscosity, the range of 0.15 to 0.8% by mass is the best, as the pour-point depressant, one having the weight-average molecular weight of preferably 10,000 to 300,000, and more preferably 50,000 to 200,000 is particularly preferable, and moreover, as the pour-point depressant, polymethacrylate-based one is particularly preferable.

Second Embodiment Method for Producing Lubricant Base Oil

The method for producing a lubricant base oil according to the second embodiment of the present invention includes

a first step of fractionating, from a hydrocarbon oil containing a base oil fraction and a heavy fraction that is heavier than the base oil fraction, the base oil fraction and the heavy fraction,

a second step of returning a cracked oil obtained by hydrocracking the heavy fraction fractionated in the first step, to the first step,

a third step of obtaining a dewaxed oil by performing hydroisomerization dewaxing of the base oil fraction,

a fourth step of obtaining a refined oil by refining the dewaxed oil, and

a fifth step of obtaining a lubricant base oil that is a hydrocarbon oil having a kinematic viscosity at 100° C. of 2.0 to 9 mm²/s, a viscosity index of 130 or more, a freezing point of −30 to −5° C., and an SBV viscosity at −20° C. of 1,000 to 60,000 mPa·s, by fractionation of the refined oil, in which

the third step is a step of performing hydroisomerization dewaxing of the base oil fraction such that the freezing point of the lubricant base oil obtained in the fifth step is higher by 10° C. or more than a freezing point of raffinate obtained by bringing the lubricant base oil into contact with urea and removing paraffin that can be included in the urea.

The base oil fraction is a fraction for obtaining a lubricant base oil after a dewaxing step, a hydrofinishing step, and a second distillation step, and the boiling point range thereof can be appropriately changed based on the intended product. Examples of the preferred boiling point range of the base oil fraction in the present embodiment include 340 to 520° C.

The heavy fraction is a fraction that has a higher boiling point than the base oil fraction. It is preferred that a boiling point of the heavy fraction is higher than 520° C.

The hydrocarbon oil may also contain, other than the base oil fraction and the heavy fraction, a fraction (light fraction) that has a lower boiling point than the base oil fraction. It is preferred that a boiling point of the light fraction is lower than 340° C.

Examples of the hydrocarbon oil include hydrotreated or hydrocracked gas oil, heavy gas oil, vacuum gas oil, lubricant oil raffinate, lubricant oil raw material, bright stock, slack wax (crude wax), foot's oil, deoiled wax, paraffinic wax, microcrystalline wax, petrolatum, synthetic oils, Fischer-Tropsch synthesis reaction oil (hereinafter referred to as an “FT synthetic oil”), high-pour-point polyolefins, and straight-chain α-olefin waxes. These hydrocarbon oils can be used singly or in combinations of two or more. In particular, the hydrocarbon oil is preferably at least one selected from the group consisting of a vacuum gas oil, a hydrocracked vacuum gas oil, an atmospheric residue, a hydrocracked atmospheric residue, a vacuum residue, a hydrocracked vacuum residue, slack wax, a dewaxed oil, paraffin wax, microcrystalline wax, petrolatum, and Fischer-Tropsch synthetic wax, and further preferably at least one selected from the group consisting of an atmospheric residue, a vacuum residue, a vacuum gas oil, slack wax, and Fischer-Tropsch synthetic wax.

In one aspect of the present invention, FT (Fischer-Tropsch) synthetic oil is preferred as the hydrocarbon oil. The FT synthetic oil is a hydrocarbon oil synthesized from carbon monoxide and hydrogen by a FT synthesis reaction, and does not contain a nitrogen content. Therefore, when the hydrocarbon oil is the FT synthetic oil, there is no possibility of sulfur poisoning in hydrocracking and isomerization dewaxing described below, and a wide variety of catalysts can be used.

Further, in another aspect of the present invention, it is preferred to use as the hydrocarbon oil a petroleum-based hydrocarbon oil containing petroleum feedstock-derived hydrocarbons. Examples of the petroleum-based hydrocarbon oil include hydrocracked vacuum gas oil, hydrocracked atmospheric residue, hydrocracked vacuum residue, slack wax, dewaxed oil, paraffinic wax, microcrystalline wax, and petrolatum.

The first step is a step of fractionating the base oil fraction and the heavy fraction from the hydrocarbon oil. Conditions of the fractionating step can be appropriately changed based on the composition of the hydrocarbon oil. For example, when the hydrocarbon oil contains 20% by volume or more of the light fraction, it is preferred that the fractionating step is carried out by atmospheric distillation for distilling away the light fraction from the hydrocarbon oil, and vacuum distillation for fractionating the base oil fraction and the heavy fraction from the bottom oil of the atmospheric distillation.

The heavy fraction fractionated in the first step is offered to the second step (hydrocracking step). The hydrocracked oil obtained in the second step is returned to the first step.

The form of a reactor used in the hydrocracking step is not particularly limited, and a fixed-bed flow reactor filled with a hydrocracking catalyst is preferably used. The reactor may be a single apparatus, or an apparatus in which a plurality of reactors are arranged in series or in parallel. Moreover, a catalyst bed in the reactor may be a single bed or a plurality of beds.

A known hydrocracking catalyst is used as a hydrocracking catalyst and it is preferred to use a catalyst (hereinafter referred to as a “hydrocracking catalyst A”) in which a metal of groups 8 to 10 of the periodic table of elements having hydrogenation activity is supported on an inorganic carrier that is a solid acid. Especially, when the hydrocarbon oil is FT synthetic oil, it is preferred to use the hydrocracking catalyst A, because there is no risk of catalyst poisoning due to sulfur content.

Examples of the inorganic carrier that is a preferred solid acid and constitutes the hydrocracking catalyst A include ones aimed from one or more inorganic compounds selected from zeolites, such as ultrastable Y-type (USY) zeolite, Y-type zeolite, mordenite, and β-zeolite, as well as amorphous composite metal oxides having heat resistance such as silica-alumina, silica-zirconia, and alumina-boria. Moreover, the carrier is more preferably a composition formed from USY zeolite and one or more amorphous composite metal oxides selected from silica-alumina, alumina-boria, and silica-zirconia, and further preferably a composition formed from USY zeolite and alumina-boria and/or silica-alumina.

USY zeolite is one obtained by ultrastabilizing Y-type zeolite by hydrothermally treatment and/or acid treatment, in which newly pores having a pore diameter within a range of 2 to 10 nm are formed in addition to the fine pore structure that Y-type zeolite inherently has and is called micropores having a pore diameter of 2 nm or less. The average particle size of the USY zeolite, which although is not especially limited, is preferably 1.0 μm or less, and more preferably 0.5 μm or less. Further, the silica/alumina molar ratio (molar ratio of silica based on alumina) in the USY zeolite is preferably 10 to 200, more preferably 15 to 100, and even more preferably 20 to 60.

It is preferred that the carrier of the hydrocracking catalyst A includes 0.1 to 80% by mass of crystalline zeolite and 0.1 to 60% by mass of amorphous composite metal oxide having heat resistance.

The carrier of the hydrocracking catalyst A can be produced by forming a carrier composition including the above-described inorganic compound that is a solid acid and the binder, and then calcining. It is preferred that the blending ratio of the inorganic compound that is a solid acid is, based on the total mass of the carrier, 1 to 70% by mass, and more preferred is 2 to 60% by mass. Further, if the carrier includes a USY zeolite, it is preferred that the blending ratio of the USY zeolite is, based on the total mass of the carrier, 0.1 to 10% by mass, and more preferred is 0.5 to 5% by mass. Still further, if the carrier includes a USY zeolite and alumina-boria, it is preferred that the blending ratio of the USY zeolite and the alumina-boria (USY zeolite/alumina-boria) is 0.03 to 1 by mass. Moreover, if the carrier includes a USY zeolite and silica-alumina, it is preferred that the blending ratio of the USY zeolite and the silica-alumina (USY zeolite/silica-alumina) is 0.03 to 1 by mass.

Although a binder is not particularly limited, alumina, silica, titania, and magnesia are preferable, and alumina is more preferable. The amount of the binder blended is, on the basis of the total mass of the carrier, preferably 20 to 98% by mass, and more preferably 30 to 96% by mass.

It is preferred that the temperature when calcining the carrier composition is in the range of 400 to 550° C., more preferred is in the range of 470 to 530° C., and even more preferred is in the range of 490 to 530° C. By calcining at such a temperature, sufficient solid acidity and mechanical strength can be imparted to the carrier.

Specifically, examples of a metal of groups 8 to 10 of the periodic table, which is supported by a carrier and has hydrogenation activity, include cobalt, nickel, rhodium, palladium, iridium, and platinum. Among them, it is preferable that metals selected from nickel, palladium, and platinum be used singly or two or more kinds thereof be used in combination. These metals may be supported on the above-described carrier by a conventional method such as impregnation or ion exchange. Although there is no particular limitation on the amount of supported metal, it is preferred that the total amount of metal is 0.1 to 3.0% by mass based on the carrier mass. Here, the term “periodic table of elements” refers to the long form periodic table of elements as stipulated by the IUPAC (the International Union of Pure and Applied Chemistry).

In the case of using the hydrocracking catalyst A, conditions when the base oil fraction is made to be brought into contact with the hydrocracking catalyst A in the presence of hydrogen are not particularly limited, and the following reaction conditions can be selected. Specifically, examples of the reaction temperature include 180 to 400° C., but the reaction temperature is preferably 200 to 370° C., more preferably 250 to 350° C., and especially preferably 280 to 350° C. If the reaction temperature is more than 400° C., not only does the yield of the base oil fraction decrease due to the base oil fraction being broken down into a light fraction, but the generated product is colored, so that usage as a fuel oil base tends to be limited. On the other hand, if the reaction temperature is less than 180° C., the hydrocracking reaction does not proceed sufficiently, so that the yield of the base oil fraction decreases. Examples of the hydrogen partial pressure include 0.5 to 12 MPa, but the hydrogen partial pressure is preferably 1.0 to 5.0 MPa. If the hydrogen partial pressure is less than 0.5 MPa, the hydrocracking tends not to proceed sufficiently. On the other hand, if the hydrogen partial pressure is more than 12 MPa, a high pressure resistance is required for the apparatus, so that equipment costs tend to increase. Examples of the liquid hourly space velocity (LHSV) of the heavy fraction include 0.1 to 10.0 h⁻¹, but the LHSV is preferably 0.3 to 3.5 h⁻¹. If the LHSV is less than 0.1 h⁻¹, the hydrocracking tends to proceed excessively, and the productivity tends to decrease. On the other hand, if the LHSV is more than 10.0 h⁻¹, the hydrocracking tends not to proceed sufficiently. Examples of the hydrogen/oil ratio include 50 to 1,000 NL/L, but the hydrogen/oil ratio is preferably 70 to 800 NL/L. If the hydrogen/oil ratio is less than 50 NL/L, the hydrocracking tends not to proceed sufficiently. On the other hand, if the hydrogen/oil ratio is more than 1,000 NL/L, large-scale hydrogen supply apparatus and the like tend to be required.

When the hydrocarbon oil is a petroleum-based hydrocarbon oil, sulfur content can be contained in the base oil fraction. In such a case, it is preferred to use, as a hydrocracking catalyst, a catalyst (hereinafter referred to as a “hydrocracking catalyst B”) having a porous inorganic oxide that includes two or more elements selected from aluminum, silicon, zirconium, boron, titanium, and magnesium, and one or more metals selected from the elements of group 6A and group 8 of the periodic table that are supported on the porous inorganic oxide. According to the hydrocracking catalyst B, decrease in the catalytic activity due to sulfur poisoning is sufficiently suppressed.

As the carrier of the hydrocracking catalyst B, as described above, a porous inorganic oxide formed from two or more selected from aluminum, silicon, zirconium, boron, titanium, and magnesium can be used. Such a porous inorganic oxide is, from the perspective of enabling a much greater improvement in the hydrocracking activity, preferably an inorganic oxide that includes two or more selected from aluminum, silicon, zirconium, boron, titanium, and magnesium, and more preferably an inorganic oxide (a composite oxide of an aluminum oxide and another oxide) that includes aluminum and another element.

If the porous inorganic oxide contains aluminum as a constituent element, the content of aluminum is preferably 1 to 97% by mass, more preferably 10 to 97% by mass, and even more preferably 20 to 95% by mass in terms of alumina, based on the total amount of the porous inorganic oxide. If the content of aluminum is less than 1% by mass in terms of alumina, physical properties such as the carrier acid properties are not preferable, and a sufficient hydrocracking activity tends not to be exhibited. On the other hand, if the content of aluminum is more than 97% by mass in terms of alumina, the catalyst surface area is insufficient and the activity tends to decrease.

The method for introducing silicon, zirconium, boron, titanium, and magnesium, which are constituent elements of the carrier other than aluminum, into the carrier is not especially limited. A solution containing these elements or the like may be used as a raw material. For example, there may be used, for silicon, silicon, liquid glass, and silica sol; for boron, boric acid; for phosphorus, phosphoric acid and an alkali metal salt of phosphoric acid; for titanium, titanium sulfide, titanium tetrachloride, and various alkoxide salts; and for zirconium, zirconium sulfate and various alkoxide salts.

Further, the porous inorganic oxide preferably contains phosphorus as a constituent element. The content of phosphorus is preferably 0.1 to 10% by mass, more preferably 0.5 to 7% by mass, and even more preferably 2 to 6% by mass based on the total amount of the porous inorganic oxide. If the content of phosphorus is less than 0.1% by mass, sufficient hydrocracking activity tends not to be exhibited, and if the content of phosphorus is more than 10% by mass, excessive cracking can proceed.

It is preferred to add the raw materials for the constituent components of the carrier other than the above-described aluminum oxide in a step before the calcining of the carrier. For example, the raw materials are added to an aluminum aqueous solution in advance and then an aluminum hydroxide gel containing these constituent components may be prepared or the raw materials may be added to the prepared aluminum hydroxide gel. Alternatively, the raw materials may be added in a step in which water or an acidic aqueous solution is added to a commercially available aluminum oxide intermediate or a boehmite powder, and the resulting mixture is kneaded. However, it is preferred that the raw materials are allowed to coexist during the stage of preparing the aluminum hydroxide gel. Although the mechanism for exhibiting the effect of the constituent components of the carrier other than aluminum oxide is not entirely understood, it is thought that the constituent components form a complex oxide state with aluminum, and that this causes an increase in the carrier surface area and interactions with the active metals to occur, thereby influencing the activity.

One or more metals selected from the elements of group 6A and group 8 of the periodic table is supported on the above-described porous inorganic oxide acting as a carrier. Among these metals, it is preferred to use a combination of two or more metals selected from cobalt, molybdenum, nickel, and tungsten. Examples of preferred combinations include cobalt-molybdenum, nickel-molybdenum, nickel-cobalt-molybdenum, and nickel-tungsten. Among these, more preferred is a combination of nickel-molybdenum, nickel-cobalt-molybdenum, and nickel-tungsten. During the hydrocracking, these metals are converted into a sulfide state to use.

As the content of the active metal based on the catalyst mass, the range of the total amount of tungsten and molybdenum supported is preferably 12 to 35% by mass, and more preferably 15 to 30% by mass, in terms of the oxide. If the total amount of tungsten and molybdenum supported is less than 12% by mass, the active sites decrease and sufficient activity tends not to be obtained. On the other hand, if the total amount of tungsten and molybdenum supported is more than 35% by mass, the metals are not effectively dispersed and sufficient activity tends not to be obtained. The range of the total amount of cobalt and nickel supported is preferably 1.0 to 15% by mass and more preferably 1.5 to 12% by mass in terms of the oxide. If the total amount of cobalt and nickel supported is less than 1.0% by mass, a sufficient co-catalyst effect is not obtained and the activity tends to decrease. On the other hand, if the total amount of cobalt and nickel supported is more than 15% by mass, the metals are not effectively dispersed and sufficient activity tends not to be obtained.

The method for incorporating these active metals into the catalyst is not especially limited. A known method that is applied when producing a general hydrocracking catalyst may be employed. Generally, it is preferred to employ a method in which a solution containing a salt of the active metal is impregnated into the catalyst carrier. In addition, an equilibrium adsorption method, a pore-filling method, an incipient-wetness method and the like can also be preferably employed. For example, a pore-filling method is a method in which the pore volume of a carrier is measured in advance and then the carrier is impregnated with the same volume of a metal salt solution. In addition, the impregnation method is not especially limited. The carrier may be impregnated by a suitable method based on the amount of the metal supported and the physical properties of the catalyst carrier.

In the present embodiment, the number of the hydrocracking catalyst B types to be used is not especially limited. For example, one type of catalyst may be used singly or a plurality of catalysts with different active metal species or carrier constituent components may be used. Examples of a suitable combination when using a plurality of different catalysts include a catalyst containing cobalt-molybdenum following on from a catalyst containing nickel-molybdenum, a catalyst containing nickel-cobalt-molybdenum following on from a catalyst containing nickel-molybdenum, a catalyst containing nickel-cobalt-molybdenum following on from a catalyst containing nickel-tungsten, and a catalyst containing cobalt-molybdenum following on from a catalyst containing nickel-cobalt-molybdenum. Prior to and/or following these combinations, a nickel-molybdenum catalyst may be further combined.

When combining a plurality of catalysts with different carrier components, a catalyst may be used that, for example, has an aluminum oxide content in the range of 80 to 99% by mass following on from a catalyst having an aluminum oxide content of 30% by mass or more and less than 80% by mass based on the total mass of the carrier.

Further, other than the hydrocracking catalyst B, a guard catalyst, a demetallization catalyst, and an inactive filler may optionally be used for the purpose of trapping the scale content which flows in along with the base oil fraction and supporting the hydrocracking catalyst B at the partition part of the catalyst bed as necessary. These may be used singly or in combinations thereof.

It is preferred that the pore volume of the hydrocracking catalyst B as measured by a nitrogen adsorption BET method is 0.30 to 0.85 ml/g, and more preferred is 0.45 to 0.80 ml/g. If the pore volume is less than 0.30 ml/g, the dispersibility of the supported metals is insufficient, and the active sites may decrease. In addition, if the pore volume is more than 0.85 ml/g, the catalyst strength is insufficient, so that the catalyst may turn into a powder and break up during use.

Further, it is preferred that the average pore size of the catalyst determined by a nitrogen adsorption BET method is 5 to 11 nm, and more preferred is 6 to 9 nm. If the average pore size is less than 5 nm, the reaction substrate is not sufficiently dispersed in the pores, and the reactivity may decrease. In addition, if the average pore size is more than 11 nm, the pore surface area decreases and the activity may become insufficient.

In addition, in the hydrocracking catalyst B, in order to maintain effective catalyst pores and exhibit sufficient activity, it is preferred that the ratio of the pore volume derived from pores having a pore diameter of 3 nm or less to the total pore volume is 35% by volume or less.

When the hydrocracking catalyst B is used, the hydrocracking conditions can be set to, for example, a hydrogen pressure of 2 to 13 MPa, a liquid hourly space velocity (LHSV) of 0.1 to 3.0 h⁻¹, and a hydrogen-oil ratio (hydrogen/oil ratio) of 150 to 1,500 NL/L, are preferably a hydrogen pressure of 4.5 to 12 MPa, a liquid hourly space velocity of 0.3 to 1.5 h⁻¹, and a hydrogen-oil ratio of 380 to 1,200 NL/L, and more preferably a hydrogen pressure of 6 to 15 MPa, a liquid hourly space velocity of 0.3 to 1.5 h⁻¹, and a hydrogen-oil ratio of 350 to 1,000 NL/L. All of these conditions are factors having an influence on the reaction activity. For example, if the hydrogen pressure and the hydrogen-oil ratio are less than the above lower limits, the reactivity tends to decrease and the activity tends to rapidly decrease. On the other hand, if the hydrogen pressure and the hydrogen-oil ratio are more than the above upper limits, an excessive investment in equipment such as a compressor tends to be required. In addition, the lower the liquid hourly space velocity is, the more advantageous it tends to be for the reaction. However, if the liquid hourly space velocity is less than the above lower limit, a reactor having an extremely large internal volume is required and an excessive investment in equipment tends to be required. On the other hand, if the liquid hourly space velocity is more than the above upper limit, the reaction tends not to sufficiently proceed. Further, the reaction temperature may be 180 to 400° C., is preferably 200 to 370° C., more preferably 250 to 350° C., and especially preferably 280 to 350° C. If the reaction temperature is more than 400° C., not only does the yield of the base oil fraction decrease due to the base oil fraction being broken down into a light fraction, but the generated product is colored, so that usage as a fuel oil base tends to be limited. On the other hand, if the reaction temperature is less than 180° C., the hydrocracking reaction does not proceed sufficiently, so that the yield of the base oil fraction decreases.

In the hydrocracking step, the heavy fraction is, due to the hydrocracking, converted into hydrocarbons having a boiling point of about 520° C. or less. On the other hand, a part of the heavy fraction is not sufficiently hydrocracked, and remains as an uncracked heavy fraction having a boiling point of 520° C. or more.

The composition of the hydrocracked oil is determined based on the hydrocracking catalyst to be used and the hydrocracking reaction conditions. Here, unless otherwise stated, the “hydrocracked oil” refers to all the products of hydrocracking, including the uncracked heavy fraction. If the hydrocracking reaction conditions are severer than necessary, although the content of the uncracked heavy fraction in the hydrocracked oil decreases, a light fraction having a boiling point of 340° C. or less increases, and the yield of the preferred base oil fraction (340 to 520° C. fraction) decreases. On the other hand, if the hydrocracking reaction conditions are milder than necessary, the content of the uncracked heavy fraction increases, and the base oil fraction yield decreases. In the case where the ratio M2/M1 of the mass M2 of the cracking products having a boiling point of 25 to 520° C. to the mass M1 of all the cracking products having a boiling point of 25° C. or more is referred to as a “cracking ratio”, generally, the reaction conditions are preferably selected such that the cracking ratio M2/M1 is 5 to 70%, preferably 10 to 60%, and further preferably 20 to 50%.

Next, the third step (dewaxing step) will be described. In the dewaxing step, the base oil fraction fractionated in the first step is brought into contact with a hydrocracking catalyst in the presence of hydrogen (molecular hydrogen). Accordingly, the base oil fraction is dewaxed by hydroisomerization to obtain a dewaxed oil. At this time, hydroisomerization dewaxing of the above-described base oil fraction is performed such that a freezing point of the lubricant base oil obtained in the fifth step described below is higher by 10° C. or more (15° C. or more in the case of producing the lubricant base oil C) than a freezing point of raffinate obtained by bringing the lubricant base oil into contact with urea and removing paraffin that can be included in the urea.

As a tube reactor for the dewaxing step, a known fixed-bed tube reactor can be used. More specifically, for example, hydroisomerization can be performed by filling a fixed-bed flow reactor with a hydroisomerization catalyst and making hydrogen (molecular hydrogen) and the base oil fraction flow through the reactor.

As the hydroisomerization catalyst, a catalyst that is generally used for hydroisomerization, namely, a catalyst in which a metal having a hydrogenation activity is supported on an inorganic carrier, can be used.

As the metal having a hydrogenation activity and constituting the hydroisomerization catalyst, one or more metals selected from the group consisting of metals of group 6, group 8, group 9, and group 10 of the periodic table of elements are used. Specific examples of these metals include noble metals such as platinum, palladium, rhodium, ruthenium, iridium, and osmium, or cobalt, nickel, molybdenum, tungsten, and iron. Preferred are platinum, palladium, nickel, cobalt, molybdenum, and tungsten, and more preferred are platinum and palladium. In addition, it is also preferred to use these metals in combinations of a plurality of species. In this case, examples of preferred combinations include platinum-palladium, cobalt-molybdenum, nickel-molybdenum, nickel-cobalt-molybdenum, and nickel-tungsten.

Examples of inorganic carriers constituting the hydroisomerization catalyst include metal oxides such as alumina, silica, titania, zirconia, and boria. These metal oxides may be one kind, a mixture of two or more kinds, or a composite metal oxide such as silica-alumina, silica-zirconia, alumina-zirconia, and alumina-boria. From the perspective of efficiently promoting the hydroisomerization of normal paraffins, the inorganic carrier is preferably a composite metal oxide that is a solid acid, such as silica-alumina, silica-zirconia, alumina-zirconia, and alumina-boria. Further, a small amount of zeolite may be included in the inorganic carrier. In order to improve the moldability and mechanical strength of the carrier, the inorganic carrier may be blended with a binder. Examples of preferred binders include alumina, silica, and magnesia.

As the content of the metal having a hydrogenation activity in the hydroisomerization catalyst, if this metal is the above-described noble metal, it is preferred that the content is about 0.1 to 3% by mass based on the mass of the carrier as metal atoms. Further, if this metal is a metal other than the above-described noble metals, it is preferred that the content is about 2 to 50% by mass based on the mass of the carrier as a metal oxide. If the content of the metal having a hydrogenation activity is less than the above-described lower limit, hydrorefining and hydroisomerization tend not to proceed sufficiently. On the other hand, if the content of the metal having a hydrogenation activity is more than the above-described upper limit, dispersion of the metal having a hydrogenation activity deteriorates, so that the activity of the catalyst tends to decrease, and the catalyst cost increases.

Further, the hydroisomerization catalyst may be a catalyst in which one or more metals selected from the elements of group 8 of the periodic table that is supported on a carrier including a porous inorganic oxide that is formed from a substance selected from aluminum, silicon, zirconium, boron, titanium, magnesium, and zeolite.

Examples of the porous inorganic oxide used as a carrier of such a hydroisomerization catalyst include alumina, titania, zirconia, boria, silica, or zeolite, and of these, preferred is a porous inorganic oxide formed from alumina and at least one of titania, zirconia, boria, silica, and zeolite. The production method is not especially limited, but an arbitrary preparation method may be employed that uses raw materials in the form of various sols or salt compounds corresponding to the respective elements. Furthermore, the carrier may be prepared by once preparing a composite hydroxide or a composite oxide, such as silica-alumina, silica-zirconia, alumina-titania, silica-titania, and alumina-boria, and then adding the composite hydroxide or composite oxide in the form of an alumina gel or other hydroxide, or in the form an appropriate solution, at an arbitrary stage of the preparation step. The proportion of alumina to the other oxide may be any ratio based on the carrier, but the content of alumina is preferably 90% by mass or less, more preferably 60% by mass or less, even more preferably 40% by mass or less, and preferably 10% by mass or more, and more preferably 20% by mass or more.

Examples of the zeolite, which is a crystalline alumino silicate, include faujasite, pentasil, mordenite, TON, MTT, and MRE. A zeolite that has been ultrastabilized by a predetermined hydrothermal treatment and/or acid treatment, or a zeolite whose alumina content has been adjusted may be used. It is preferred to use faujasite or mordenite, and especially preferred to use a Y or beta type. The Y type is preferably ultrastabilized. A zeolite ultrastabilized by a hydrothermal treatment has, in addition to its inherent pore structure, called micropores, of 20 angstroms or less, newly formed pores in the range of 20 to 100 angstroms. The hydrothermal treatment may be carried out under known conditions.

As the active metal of such a hydroisomerization catalyst, one or more metals selected from the elements of group 8 of the periodic table can be used. Among these metals, preferably used are one or more metals selected from Pd, Pt, Rh, Ir, Au and Ni, and more preferably used is a combination thereof. Examples of a preferred combination include Pd—Pt, Pd—Ir, Pd—Rh, Pd—Au, Pd—Ni, Pt—Rh, Pt—Ir, Pt—Au, Pt—Ni, Rh—Ir, Rh—Au, Rh—Ni, Ir—Au, Ir—Ni, Au—Ni, Pd—Pt—Rh, Pd—Pt—Ir, and Pt—Pd—Ni. Among these, more preferred combinations are Pd—Pt, Pd—Ni, Pt—Ni, Pd—Ir, Pt—Rh, Pt—Ir, Rh—Ir, Pd—Pt—Rh, Pd—Pt—Ni, and Pd—Pt—Ir, and even more preferred combinations are Pd—Pt, Pd—Ni, Pt—Ni, Pd—Ir, Pt—Ir, Pd—Pt—Ni, and Pd—Pt—Ir.

The total content of the active metals is preferably 0.1 to 2% by mass, more preferably 0.2 to 1.5% by mass, and even more preferably 0.5 to 1.3% by mass, in terms of metal, based on catalyst mass. If the total amount of metals supported is less than 0.1% by mass, the number of active sites is reduced, so that sufficient activity tends not to be obtained. On the other hand, if the total amount of metals supported is more than 2% by mass, the metals are not dispersed effectively, so that sufficient activity tends not to be obtained.

For any of the above-described hydroisomerization catalysts, the method for supporting the active metal on the carrier is not especially limited. A known method that is applied when producing a general hydroisomerization catalyst may be employed. Generally, it is preferred to employ a method in which a solution containing a salt of the active metal is impregnated into the catalyst carrier. In addition, an equilibrium adsorption method, a pore-filling method, an incipient-wetness method and the like can also be preferably employed. For example, a pore-filling method is a method in which the pore volume of a carrier is measured in advance and then the carrier is impregnated with the same volume of a metal salt solution. Although the impregnation method is not especially limited, the carrier may be impregnated by a suitable method based on the amount of the metal supported and the physical properties of the catalyst carrier.

As the hydroisomerization catalyst, the following catalyst can also be used.

<Specific Aspect of the Hydroisomerization Catalyst>

The hydroisomerization catalyst according to this aspect is imparted with its characteristics as a result of being produced by a specific method. The hydroisomerization catalyst according to the present aspect will now be described with reference to a preferred production aspect thereof.

The method for producing the hydroisomerization catalyst according to the present aspect includes a first step of obtaining a carrier precursor by heating a mixture that includes an ion-exchanged zeolite obtained by ion-exchanging an organic template-containing zeolite that contains an organic template and has a one-dimensional, 10-membered ring pore structure in a solution containing ammonium ions and/or protons, and a binder, in a N₂ atmosphere at a temperature of 250 to 300° C., and a second step of obtaining a hydroisomerization catalyst in which platinum and/or palladium is supported on a carrier including zeolite by calcining a catalyst precursor incorporating a platinum salt and/or palladium salt in the carrier precursor in an atmosphere containing molecular oxygen at a temperature of 350 to 400° C.

From the perspective of achieving a high level of both high isomerization activity and suppressed cracking activity in the hydroisomerization reactions of normal paraffins, the organic template-containing zeolite used in the present aspect has a one-dimensional pore structure formed from a 10-membered ring. Examples of such zeolites include AEL, EUO, FER, HEU, MEL, MFI, NES, TON, MTT, WEI, *MRE, and SSZ-32. The above three-lettered acronyms represent framework-type codes assigned to various structures of classified molecular sieve-type zeolites by the Structure Commission of the International Zeolite Association. It is also noted that zeolites having the same topology are collectively designated by the same code.

Among the above-described zeolites having a one-dimensional, 10-membered ring pore structure, from the perspective of high isomerization activity and low cracking activity, preferred as the organic template-containing zeolite are zeolites having a TON or an MTT structure, zeolite ZSM-48, which is a zeolite having a *MRE structure, and zeolite SSZ-32. Zeolite ZSM-22 is more preferred among zeolites having the TON structure, and zeolite ZSM-23 is more preferred among zeolites having the MTT structure.

The organic template-containing zeolite is hydrothermally synthesized according to a known method from a silica source, an alumina source, and an organic template that is added to build the above-described predetermined pore structure.

The organic template is an organic compound having an amino group, an ammonium group and the like, and is selected according to the structure of the zeolite to be synthesized. However, it is preferred that the organic template is an amine derivative. Specifically, the organic template is preferably at least one selected from the group consisting of alkylamines, alkyldiamines, alkyltriamines, alkyltetramines, pyrrolidine, piperazine, aminopiperazine, alkylpentamines, alkylhexamines, and their derivatives.

The molar ratio of the silicon element to aluminum element ([Si]/[Al]; hereinafter referred to as a “Si/Al ratio”) that constitute the organic template-containing zeolite having a one-dimensional, 10-membered ring pore structure is preferably 10 to 400, and more preferably 20 to 350. If the Si/Al ratio is less than 10, although the activity for the conversion of normal paraffins increases, the isomerization selectivity to isoparaffins decreases, and cracking reactions caused by an increase in the reaction temperature tend to sharply increase, which is undesirable. Conversely, if the Si/Al ratio is more than 400, the catalytic activity needed for the conversion of normal paraffins cannot be easily obtained, which is undesirable.

The synthesized organic template-containing zeolite, which has preferably been washed and dried, typically has alkali metal cations as counter cations, and incorporates the organic template in its pore structure. The zeolite containing an organic template, which is used for producing the hydroisomerization catalyst according to the present invention, is preferably in such a synthesized state, i.e., preferably, the zeolite has not been subjected to a calcining treatment for removing the organic template incorporated therein.

The organic template-containing zeolite is next ion-exchanged in a solution containing ammonium ions and/or protons. By the ion-exchange treatment, the counter cations contained in the organic template-containing zeolite are exchanged for ammonium ions and/or protons. Further, at the same time, a portion of the organic template incorporated in the organic template-containing zeolite is removed.

The solution used for the ion-exchange treatment is preferably a solution that uses a solvent containing at least 50% by volume of water, and more preferably is an aqueous solution. Examples of compounds for supplying ammonium ions into the solution include various inorganic and organic ammonium salts, such as ammonium chloride, ammonium sulfate, ammonium nitrate, ammonium phosphate, and ammonium acetate. On the other hand, mineral acids such as hydrochloric acid, sulfuric acid, and nitric acid are typically used as compounds for supplying protons into the solution. The ion-exchanged zeolite (here, an ammonium-form zeolite) obtained by ion exchange of the organic template-containing zeolite in the presence of ammonium ions releases ammonia during subsequent calcination, and the counter cations are converted into protons to form Bronsted acid sites. Ammonium ions are preferred as the cationic species used for the ion exchange. The amount of ammonium ions and/or protons contained in the solution is preferably set to 10 to 1,000 equivalents based on the total amount of the counter cations and organic template contained in the organic template-containing zeolite used.

The ion-exchange treatment may be performed on the organic template-containing zeolite simple substance in powder form, or alternatively, prior to the ion-exchange treatment, the organic template-containing zeolite may be blended with an inorganic oxide, which is a binder, and molded, and the ion-exchange treatment may be performed on the resulting molded body. However, if the molded body is subjected to the ion-exchange treatment in an uncalcined state, problems such as the molded body collapsing and turning into a powder tend to occur. Therefore, it is preferred to subject the organic template-containing zeolite in powder form to an ion-exchange treatment.

The ion-exchange treatment is preferably performed based on a standard method, i.e., a method in which the zeolite containing an organic template is dipped in a solution, preferably an aqueous solution, containing ammonium ions and/or protons, and the solution is stirred or fluidized. It is preferred to perforin the stirring or fluidization under heating to increase the ion-exchange efficiency. In the present aspect, especially preferred is a method in which the aqueous solution is heated, boiled, and ion-exchanged under reflux.

Further, from the perspective of increasing the ion-exchange efficiency, during the ion exchange of the zeolite in a solution, it is preferred to exchange the solution with a fresh one once or twice or more, and more preferably exchanged with a fresh one once or twice. When exchanging the solution once, the ion-exchange efficiency can be improved by, for example, dipping the organic template-containing zeolite in a solution containing ammonium ions and/or protons, and heating the solution under reflux for 1 to 6 hours, followed by exchanging the solution with a fresh one, and further heating under reflux for 6 to 12 hours.

By the ion-exchange treatment, substantially all of the counter cations such as an alkali metal in the zeolite can be exchanged for ammonium ions and/or protons. On the other hand, regarding the organic template incorporated in the zeolite, although a portion of the organic template is removed by the ion-exchange treatment, it is generally difficult to remove all of the organic template even if the ion-exchange treatment is repeatedly performed, so that a portion of the organic template remains inside the zeolite.

In the present aspect, a carrier precursor is obtained by heating a mixture in which the ion-exchanged zeolite and the binder are included in a nitrogen atmosphere at a temperature of 250 to 350° C.

The mixture in which the ion-exchanged zeolite and the binder are included is preferably obtained by blending an inorganic oxide, which is a binder, with the ion-exchanged zeolite obtained by the above-described method, and molding the resulting composition to folia a molded body. The purpose of blending an inorganic oxide with the ion-exchanged zeolite is to increase the mechanical strength of the carrier (in particular, a particulate carrier) obtained by calcining the molded body to a degree that can withstand practical applications. However, the present inventor found that the selection of the type of inorganic oxide affects the isomerization selectivity of the hydroisomerization catalyst. From this perspective, at least one inorganic oxide selected from alumina, silica, titania, boria, zirconia, magnesia, ceria, zinc oxide, phosphorus oxide, and a composite oxide containing a combination of two or more of these oxides can be used as the inorganic oxide. Among the above, silica and alumina are preferred, and alumina is more preferred, from the perspective of further improving the isomerization selectivity of the hydroisomerization catalyst. The phrase “composite oxide containing a combination of two or more of these oxides” refers to a composite oxide containing at least two components from alumina, silica, titania, boria, zirconia, magnesia, ceria, zinc oxide, and phosphorus oxide, but is preferably an alumina-based composite oxide containing 50% by mass or more of an alumina component based on the composite oxide, and among those, is more preferably alumina-silica.

The blending ratio of the ion-exchanged zeolite and the inorganic oxide in the above-described composition is preferably 10:90 to 90:10, and more preferably 30:70 to 85:15, in terms of the mass ratio of the ion-exchanged zeolite to the inorganic oxide. If this ratio is less than 10:90, the activity of the hydroisomerization catalyst tends to be insufficient, which is undesirable. Conversely, if the ratio is more than 90:10, the mechanical strength of the carrier obtained by molding and calcining the composition tends to be insufficient, which is undesirable.

Although the method for blending the inorganic oxide with the ion-exchanged zeolite is not especially limited, a general method can be employed, such as, for example, a method in which a suitable amount of a liquid such as water is added to the powders of both components to form a viscous fluid, and the fluid is kneaded in a kneader or the like.

The composition containing the ion-exchanged zeolite and inorganic oxide, or a viscous fluid including the composition, is molded by a method such as extrusion molding, and is preferably dried, to form a particulate molded body. Although the shape of the molded body is not especially limited, examples of the shape include a cylindrical shape, a pellet shape, a spherical shape, and an irregular tubular shape having a three leaf shaped or a four leaf shaped cross-section. Although the size of the molded body is not especially limited, the molded body is preferably, for example, about 1 to 30 mm in the long axis, and about 1 to 20 mm in the short axis, from the perspective of the ease of handling, the load density in the reactor and the like.

In the present aspect, it is preferred to form the carrier precursor by heating the thus-obtained molded body in a N₂ atmosphere at a temperature of 250 to 350° C. Regarding the heating time, preferred is 0.5 to 10 hours, and more preferred is 1 to 5 hours.

In the present aspect, if the above-described heating temperature is less than 250° C., a large amount of organic template remains, and the zeolite pores become blocked with the remaining template. The isomerization active sites are thought to exist near the pore mouth. Thus, in the above case, the reaction substrate cannot disperse into the pores due to the pore blockage, so that the active sites become covered, the isomerization reaction does not easily proceed, and a normal paraffin conversion rate tends not to be sufficiently obtained. On the other hand, if the heating temperature is more than 350° C., the isomerization selectivity of the obtained isomerization catalyst does not sufficiently improve.

It is preferred that the lower limit for the temperature when forming the carrier precursor by heating the molded body is 280° C. or more, and that the upper limit for the temperature is 330° C. or less.

In the present aspect, it is preferred to heat the above-described mixture so that a portion of the organic template included in the molded body remains. Specifically, it is preferred to set the heating conditions so that the micropore volume per unit mass of the hydroisomerization catalyst obtained by calcining after the below-described metal supporting is 0.02 to 0.11 cc/g, and the micropore volume per unit mass of the zeolite that is contained in that catalyst is 0.04 to 0.12 cc/g.

Next, the catalyst precursor incorporating a platinum salt and/or palladium salt in the above-described carrier precursor is calcined in an atmosphere containing molecular oxygen at a temperature of 350 to 400° C., preferably 380 to 400° C., and more preferably 400° C., to obtain a hydroisomerization catalyst in which a platinum and/or palladium is supported on a carrier including zeolite. Here, “in an atmosphere containing molecular oxygen” means bringing into contact with a gas including oxygen gas, and of those preferably air. The calcining time is preferably 0.5 to 10 hours, and more preferably 1 to S hours.

Examples of the platinum salt include chloroplatinic acid, tetraammineplatinum dinitrate, dinitroaminoplatinum, and tetraamminedichloroplatinum. Since chloride salts can produce hydrochloric acid during a reaction, which may cause apparatus corrosion, tetraammineplatinum dinitrate, which is a platinum salt that is not a chloride salt and in which a high level of platinum is dispersed, is preferred.

Examples of the palladium salt include palladium chloride, tetraammine palladium nitrate, and diaminopalladium nitrate. Since chloride salts can produce hydrochloric acid during a reaction, which may cause apparatus corrosion, tetraammine palladium nitrate, which is a palladium salt that is not a chloride salt and in which a high level of palladium is dispersed, is preferred.

The amount of the active metal supported on the carrier including zeolite according to the present aspect is preferably 0.001 to 20% by mass, and more preferably 0.01 to 5% by mass, based on the mass of the carrier. If the amount supported is less than 0.001% by mass, it is difficult to impart a predetermined hydrogenation/dehydrogenation function to the catalyst. Conversely, if the amount supported is more than 20% by mass, conversion on the active metal of hydrocarbons into lighter products by cracking tends to proceed, so that the yield of the intended fraction tends to decrease, and the catalyst costs tend to increase, which are undesirable.

Further, when the hydroisomerization catalyst according to the present aspect is used for hydroisomerization of a hydrocarbon oil containing many sulfur-containing compounds and/or nitrogen-containing compounds, from the perspective of the durability of catalytic activity, it is preferred that the active metals are a combination such as nickel-cobalt, nickel-molybdenum, cobalt-molybdenum, nickel-molybdenum-cobalt, or nickel-tungsten-cobalt. It is preferred that the amount of these metals supported is 0.001 to 50% by mass, and more preferably 0.01 to 30% by mass, based on the mass of the carrier.

In the present aspect, it is preferred to calcine the above-described catalyst precursor so that the organic template remaining in the carrier precursor remains. Specifically, it is preferred to set the heating conditions so that the micropore volume per unit mass of the obtained hydroisomerization catalyst is 0.02 to 0.11 cc/g, and the micropore volume per unit mass of the zeolite that is contained in that catalyst is 0.04 to 0.12 cc/g.

The micropore volume per unit mass of the hydroisomerization catalyst is calculated by a method called nitrogen adsorption measurement. Namely, for the catalyst, the micropore volume per unit mass of the catalyst is calculated by analyzing a physical adsorption and desorption isotherm of nitrogen measured at the temperature of liquid nitrogen (−196° C.), specifically, analyzing an adsorption isotherm of nitrogen measured at the temperature of liquid nitrogen (−196° C.) by a t-plot method. Further, the micropore volume per unit mass of the zeolite contained in the catalyst is also calculated by the above-described nitrogen adsorption measurement.

In addition, in the present description, a micropore indicates a “pore having a diameter of 2 nm or less” defined in IUPAC (International Union of Pure and Applied Chemistry).

A micropore volume V_(z) per unit mass of the zeolite contained in the catalyst can be calculated, for example, if the binder does not have a micropore volume, based on the following expression from a value V_(c) of the micropore volume per unit mass of the hydroisomerization catalyst and the content M_(z) (% by mass) of zeolite in the catalyst.

V _(z) =V _(c) /M _(z)×100

It is preferred that, subsequent to the calcination treatment, the hydroisomerization catalyst of the present aspect is subjected to a reduction treatment after the catalyst is loaded in the reactor for conducting the hydroisomerization reaction. Specifically, it is preferred that the hydroisomerization catalyst is subjected to the reduction treatment for about 0.5 to 5 hours in an atmosphere containing molecular hydrogen, and preferably under a stream of hydrogen gas, preferably at 250 to 500° C., and more preferably at 300 to 400° C. By performing this step, it can be further ensured that high activity for the dewaxing of the hydrocarbon oil can be imparted to the catalyst.

The hydroisomerization catalyst according to the present aspect is a hydroisomerization catalyst containing a carrier that includes a zeolite having a one-dimensional, 10-membered ring pore structure and a binder, and platinum and/or palladium supported on the carrier, in which the micropore volume per unit mass of the catalyst is 0.02 to 0.11 cc/g. Further, this zeolite is preferably a zeolite derived from ion-exchanged zeolite obtained by ion-exchanging an organic template-containing zeolite that contains an organic template and has a one-dimensional, 10-membered ring pore structure in a solution containing ammonium ions and/or protons, in which the micropore volume per unit mass of the zeolite contained in the catalyst is 0.04 to 0.12 cc/g.

The above-described hydroisomerization catalyst can be produced by the method described above. The micropore volume per unit mass of the catalyst and the micropore volume per unit mass of the zeolite contained in the catalyst can be set to be within the above-described ranges by appropriately adjusting the amount of ion-exchanged zeolite blended in the mixture including the ion-exchanged zeolite and a binder, the heating conditions of the mixture in a N₂ atmosphere, and the heating conditions of the catalyst precursor in the atmosphere containing molecular oxygen.

The reaction temperature in the dewaxing step is preferably 200 to 450° C., and more preferably 220 to 400° C. If the reaction temperature is less than 200° C., the isomerization of the normal paraffins contained in the base oil fraction tends not to easily proceed, so that the reduction and removal of the wax component tend to be insufficient. Conversely, if the reaction temperature is more than 450° C., cracking of the base oil fraction is significant, so that the yield of the lubricant base oil tends to decrease.

The reaction pressure in the dewaxing step is preferably 0.1 to 20 MPa, and more preferably 0.5 to 15 MPa. If the reaction pressure is less than 0.1 MPa, catalyst degradation due to the formation of coke tends to be accelerated. Conversely, if the reaction pressure is more than 20 MPa, construction costs for the apparatus increase, so that it tends to become difficult to realize an economical process.

In the dewaxing step, the liquid hourly space velocity of the base oil fraction based on the catalyst is preferably 0.01 to 100 hr⁻¹, and more preferably 0.1 to 50 hr⁻¹. If the liquid hourly space velocity is less than 0.01 hr⁻¹, the cracking of the base oil fraction tends to proceed excessively, so that production efficiency tends to decrease. Conversely, if the liquid hourly space velocity is more than 100 hr⁻¹, the isomerization of the normal paraffins contained in the base oil fraction tends not to proceed easily, so that the reduction and removal of the wax component tend to be insufficient.

The supply ratio of hydrogen to base oil fraction is preferably 100 to 1,000 Nm³/m³, and more preferably 200 to 800 Nm³/m³. If the supply ratio is less than 100 Nm³/m³, for example, when the base oil fraction contains sulfur or nitrogen content, hydrogen sulfide and ammonia gas produced by desulfurization and denitrification reactions that accompany the isomerization reaction are adsorbed onto and poison the active metal on the catalyst, which tends to make it difficult to achieve a predetermined catalytic performance. Conversely, if the supply ratio is more than 1,000 Nm³/m³, hydrogen supply equipment having an increased capacity is required, which tends to make it difficult to realize an economical process.

The dewaxed oil obtained in the dewaxing step is offered to the fourth step (hydrofinishing step), and hydrofinishing treatment (hydrorefining treatment) is performed.

A reactor used in the hydrofinishing step is not particularly limited, and the hydrofinishing treatment (hydrorefining treatment) can be suitably performed by filling a fixed-bed flow reactor with a predetermined hydrorefining catalyst and making molecular hydrogen and the above-described dewaxed oil flow through the reactor. The hydrofinishing treatment (hydrorefining treatment) described herein means improvement in oxidation stability and a hue of the lubricant oil, and olefin hydrogenation and aromatic hydrogenation of the dewaxed oil are performed.

Examples of the hydrorefining catalyst include catalysts that include a carrier including one or more inorganic solid acidic substances selected from alumina, silica, zirconia, titania, boria, magnesia, and phosphorus, and one or more active metals selected from the group consisting of platinum, palladium, nickel-molybdenum, nickel-tungsten, and nickel-cobalt-molybdenum that is supported on the carrier.

A preferred carrier is an inorganic solid acidic substance that includes at least two or more of alumina, silica, zirconia, or titania.

As the method for supporting the active metals on the carrier, a conventional method such as impregnation or ion exchange may be employed.

The amount of the active metals supported in the hydrorefining catalyst is preferably such that the total amount of metal is 0.1 to 25% by mace based on the carrier.

The average pore size of the hydrorefining catalyst is preferably 6 to 60 nm, and more preferably 7 to 30 nm. If the average pore size is less than 6 nm, a sufficient catalytic activity tends not to be obtained, while if the average pore size is more than 60 nm, catalytic activity tends to decrease due to a decrease in the level of dispersion of the active metals. Further, it is preferred that the pore volume of the hydrorefining catalyst is 0.2 mL/g or more. If the pore volume is less than 0.2 mL/g, degradation of the activity of the catalyst tends to occur earlier. In addition, it is preferred that the specific surface area of the hydrorefining catalyst is 200 m²/g or more. If the specific surface area of the catalyst is less than 200 m²/g, the dispersibility of the active metals is insufficient, so that activity tends to decrease. The pore volume and the specific surface area of the catalyst can be measured and calculated by a BET method using nitrogen adsorption.

It is preferred that the reaction conditions in the hydrofinishing step are set to a reaction temperature of 200 to 300° C., a hydrogen partial pressure of 3 to 20 MPa, an LHSV of 0.5 to 5 h-1, and a hydrogen/oil ratio of 1000 to 5000 sctb, and more preferred are a reaction temperature of 200° C. to 300° C., a hydrogen partial pressure of 4 to 18 MPa, an LHSV of 0.5 to 4 h-1, and a hydrogen/oil ratio of 2000 to 5000 scfb.

In the present embodiment, it is preferred to adjust the reaction conditions so that the sulfur and nitrogen content in the hydrorefined oil is 5 ppm by mass or less and 1 ppm by mass or less, respectively.

The refined oil obtained by the hydrofinishing step is offered to the fifth step (fractionating step). Then, a desired lubricant nil fraction is obtained by setting a plurality of cut points and performing vacuum distillation of the hydrorefined oil.

In addition, the hydrorefined oil may contain light fractions such as naphtha and kerosene and gas oil produced as a byproduct by the hydroisomerization and the hydrofinishing treatment (hydrorefining treatment), and these light fractions can be collected as a fraction having a boiling point of 350° C. or less, for example.

The method for producing a lubricant base oil of the present invention is not limited to the above-described embodiments, and can be appropriately changed. For example, the method for producing a lubricant base oil of the present invention may include a distillation step of obtaining a lubricant oil fraction by fractionating the dewaxed oil obtained by the above-described producing method of the dewaxed oil, and a hydrofinishing step of performing hydrofinishing treatment (hydrorefining treatment) of the lubricant oil fraction obtained in the distillation step.

EXAMPLES

Hereinafter, the present invention will be described more specifically based on examples and comparative examples, but the present invention is not limited to the following examples.

Examples 1 to 3, Comparative Examples 1 and 2

In Examples 1 to 3 and Comparative Examples 1 and 2, lubricant base oils shown in Table 1 were each prepared. The lubricant base oils in Examples 1 to 3 are obtained based on the method for producing a lubricant base oil according to the above-described embodiment. In contrast, the lubricant base oils in Comparative Examples 1 and 2 are obtained by the conventional method for producing a lubricant base oil. Various characteristics of the respective base oils, and the traction coefficients measured under conditions of a load of 50 N (average hertz pressure 0.60 GPa), a sample oil temperature of 50° C., a circumferential velocity of 1 m/s, and a slip ratio of 3%, and using a 27.4 mm steel ball and a steel disc are shown in Table 1.

TABLE 1 Comparative Comparative Raw materials Example 1 Example 2 Example 3 Example 1 Example 2 General physical properties Density, g/cm³ 0.8182 0.8181 0.8083 0.8180 0.8184 Flash point, ° C. 232 234 228 238 220 Kinematic viscosity, mm²/s (40° C.) 16.6 17.0 17.1 16.9 17.0 (100° C.) 4.09 4.13 4.10 4.16 4.10 Viscosity index 154 151 146 157 141 Pour point, ° C. −5 −12.5 −17.5 −2.5 −25 Freezing point, ° C. −5 −15 −20 −4 −26 NOACK, mass % (250° C.) 11.5 12.0 12.8 12.2 11.8 Sulfur content, mass ppm <1 <1 <1 <1 <1 Chromatography analysis Saturated content, mass % 99.4 99.3 99.5 99.4 99.6 Resin content, mass % 0.4 0.3 0.2 0.4 0.2 Aromatic content, mass % 0.2 0.4 0.3 0.3 0.2 Recovery rate, mass % 100 100 100 100 100 Urea adduct Adduct amount, mass % 3.18 2.72 2.08 4.05 1.15 Characteristics of raffinate Kinematic viscosity, mm²/s (40° C.) 16.50 17.04 17.02 16.84 16.98 (100° C.) 4.059 4.122 4.09 4.120 4.074 Viscosity index 153 150 146 153 142 Pour point, ° C. −27.5 −30 −30 −22.5 −30 Freezing point, ° C. −30 −32 −31 −23 −32 ΔFreezing point, ° C. −25 −17 −11 −19 −6 (Base oil-raffinate) Low-temperature characteristics CCS viscosity (−30° C.), mPa · s 870 880 630 990 141 (−35° C.), mP · s 1,650 1,600 1,590 1,950 1,530 SBV viscosity (−20° C.), mPa · s 57,600 12,000 3,200 62,000 810 (−30° C.), mPa · s 478,000 156,000 51,000 880,000 3,370 (−35° C.), mPa · s 783,000 492,000 118,000 >1,000,000 9,150 ¹³C-NMR CH 6.6 6.8 7.2 6.4 7.4 CH2 79.1 78.8 78.3 79.5 78.1 CH3 14.3 14.4 14.5 14.1 14.5 CH2 main chain 19.8 18.6 15.2 22.0 14.7 EI-MS Paraffins 92.2 92.3 92.1 92.0 92.8 Monocyclic cycloparaffin 3.8 4.5 4.2 4.6 4.0 Bicyclic cycloparaffin 3.1 2.3 2.7 2.3 2.5 Tricyclic cycloparaffin 0.3 0.2 0.1 0.3 0.2 Tetracyclic cycloparaffin 0.0 0.0 0.0 0.2 0.0 Pentacyclic cycloparaffin 0.2 0.1 0.1 0.0 0.1 Hexacyclic cycloparaffin 0.4 0.6 0.5 0.6 0.4 Alkylbenzenes 0.0 0.0 0.0 0.0 0.0 FD-MS Paraffins 61.1 58.1 50.2 65.3 65.2 Monocyclic cycloparaffin 31.4 34.6 39.9 28.5 29.2 Bicyclic cycloparaffin 6.3 6.6 7.1 5.5 4.4 Tricyclic cycloparaffin 0.5 0.6 2.3 0.4 0.4 Tetracyclic cycloparaffin 0.3 0.0 0.2 0.0 0.0 Pentacyclic cycloparaffin 0.1 0.0 0.0 0.0 0.0 Hexacyclic cycloparaffin 0.3 0.1 0.3 0.3 0.8 Traction coefficient 50N, 50° C., 1 m/s, Slip ratio 3% 0.012 0.013 0.015 0.011 0.018

Examples 4 to 6, Comparative Examples 3 to 5

In Examples 4 to 6 and Comparative Examples 3 and 4, lubricant oil compositions were prepared by adding 10% by mass of a package additive (breakdown: 40% by mass of ashless dispersant, 40% by mass of detergent, 10% by mass of antiwear agent, 8% by mass of antioxidant, and 2% by mass of metal deactivating agent) and 5% by mass of a viscosity index improver (polymethacrylate-based, Mw 350,000, effective concentration 50% by mass) to the respective lubricant base oils of Examples 1 to 3 or Comparative Examples 1 and 2, respectively. Moreover, as Comparative Example 3, a commercial 0W-20 oil was prepared. The kinematic viscosities and the viscosity indexes of the respective lubricant oil compositions are shown in Table 2.

[JC08 Cold Mode Fuel Consumption Evaluation Test]

With respect to the lubricant oil compositions of Examples 4 to 6, and Comparative Examples 3 and 4, a JC08 cold mode fuel consumption evaluation test was performed according to the following procedure.

JC08 mode is a method for measuring fuel consumption of vehicles, established by Ministry of Land, Infrastructure, Transport and

Tourism (for details, refer to Ministry of Land, Infrastructure, Transport and Tourism, Announcement that Prescribes Details of Safety Standards for Road Trucking Vehicles [2009.07.30] Attachment 42 Measurement Method of Exhaust Gas of Light and Middle Vehicles). JC08 is classified into a cold mode that starts in an engine cold state and a hot mode that measures fuel consumption in an engine warm state. In the test, a 2.5 L, FF gasoline engine vehicle (Toyota ESTIMA) was selected, the engine was washed and filled with a newly-prepared sample oil before the start of the test, the test vehicle was made to warm up at a constant rate of 60±2 km/h for 15 minutes or more on a chassis dynamometer, and then, was quickly returned to the idling state, the vehicle was driven one time in a predetermined running pattern, and then, was left (soak) in the stopped state in a room of 298±5K (25±5° C.) for 6 hours or more and 36 hours or less, and then, was driven in a predetermined pattern, and consumed fuel was calculated from driving exhaust gas to determine fuel consumption. The obtained results are shown in Table 2.

TABLE 2 Comparative Comparative Comparative Example 4 Example 5 Example 6 Example 3 Example 4 Example 5 Base Kind Example 1 Example 2 Example 3 Comparative Comparative Commercial oil Example 1 Example 2 0W-20 oil Content (% Balance Balance Balance Balance Balance by mass) Package additive 10 10 10 10 10 (% by mass) Viscosity index 5 5 5 5 5 improver (% by mass) Characteristics of compounded oil (0W-20) Kinematic viscosity, 32.6 35.5 36.0 33.8 36.6 38.8 mm²/s (40° C.) Viscosity index 246 230 225 248 222 235 JC08 cold mode fuel 4.47 3.76 3.49 0.24 0.59 — consumption Rate of fuel consumption improvement, %

Examples 7 and 8, Comparative Examples 6 to 8

In Examples 7 and 8 and Comparative Examples 6 to 8, lubricant base oils shown in Table 3 were each prepared. The lubricant base oils in Examples 7 and 8 are obtained based on the method for producing a lubricant base oil according to the above-described embodiment. In contrast, the lubricant base oils in Comparative Examples 6 to 8 are obtained by the conventional method for producing a lubricant base oil. Various characteristics of the respective base oils, and the traction coefficients measured under conditions of a load of 50 N (average hertz pressure 0.60 GPa), a sample oil temperature of 50° C., a circumferential velocity of 1 m/s, and a slip ratio of 3%, and using a 27.4 min steel ball and a steel disc are shown in Table 3.

TABLE 3 Comparative Comparative Comparative Raw materials Example 7 Example 8 Example 6 Example 7 Example 8 General physical properties Density, g/cm³ 0.8273 0.8272 0.8270 0.8260 0.8288 Flash point, ° C. 262 260 264 250 254 Kinematic viscosity, mm²/s (40° C.) 30.3 28.2 29.4 26.0 30.8 (100° C.) 6.30 5.92 6.20 5.48 6.07 Viscosity index 165 162 167 154 148 Pour point, ° C. −5 −12.5 −2.5 −15 −30 Freezing point, ° C. −5 −14 −4 −17 −32 Sulfur content, mass ppm <1 <1 <1 <1 <1 Chromatography analysis Saturated content, mass % 99.2 99.2 99.3 99.5 99.4 Resin content, mass % 0.4 0.3 0.3 0.2 0.2 Aromatic content, mass % 0.4 0.5 0.4 0.3 0.4 Recovery rate, mass % 100 100 100 100 100 Urea adduct Adduct amount, mass % 1.25 0.77 2.33 0.11 0.13 Characteristics of raffinate Kinematic viscosity, mm²/s (40° C.) 30.11 27.99 29.31 26.03 30.65 (100° C.) 6.249 5.910 6.111 5.486 6.052 Viscosity index 164 163 163 155 148 Pour point, ° C. −22.5 −25 −12.5 −25 −32.5 Freezing point, ° C. −23 −27 −13 −28 −33 ΔFreezing point, ° C. 18 13 9 9 1 (Base oil-rafflnate) Low-temperature characteristics CCS viscosity (−30° C.), mPa · s 790 880 1,070 995 1,020 (−35° C.), mP · s 1,210 1,320 1,780 1,625 1,850 SBV viscosity (−20° C.), mP · s 29,000 3,200 122,000 2,100 1,030 (−25° C.), mP · s 470,000 5,300 >1,000,000 4,300 1,700 ¹³C-NMR CH 6.2 6.5 6.0 7.1 6.8 CH2 82.0 81.5 83.2 79.8 80.0 CH3 11.2 12.0 10.8 13.1 13.2 CH2 main chain 25.3 20.3 25.9 18.0 16.0 EI-MS Paraffins 81.2 80.1 82.6 83.2 80.0 Monocyclic cycloparaffin 12.9 13.4 11.8 11.0 12.7 Bicyclic cycloparaffin 4.8 5.0 3.9 4.3 5.3 Tricyclic cycloparaffin 0.9 1.0 0.8 0.6 1.1 Tetracyclic cycloparaffin 0.1 0.1 0.1 0.1 0.2 Pentacyclic cycloparaffin 0.0 0.0 0.2 0.2 0.2 Hexacyclic cycloparaffin 0.1 0.4 0.6 0.6 0.5 Alkylbenzenes 0.0 0.0 0.0 0.0 0.0 FD-MS Paraffins 36.8 39.7 35.9 47.2 49.4 Monocyclic cycloparaffin 46.9 44.1 47.2 41.2 39.5 Bicyclic cycloparaffin 13.8 13.0 14.1 9.7 8.7 Tricyclic cycloparaffin 2.1 2.4 2.2 1.4 1.2 Tetracyclic cycloparaffin 0.1 0.2 0.2 0.1 0.1 Pentacyclic cycloparaffin 0.0 0.0 0.0 0.1 0.2 Hexacyclic cycloparaffin 0.3 0.6 0.4 0.3 0.9 Traction coefficient 50N, 25° C., 0.5 m/s. Slip ratio 3% 0.017 0.016 0.014 0.018 0.022

Examples 9 and 10, Comparative Examples 9 to 11

In Examples 9 and 10 and Comparative Examples 9 to 11, lubricant oil compositions were prepared by adding 10% by mass of a package additive (breakdown: 40% by mass of ashless dispersant, 40% by mass of detergent, 10% by mass of antiwear agent, 8% by mass of antioxidant, and 2% by mass of metal deactivating agent) and 5% by mass of a viscosity index improver (polymethacrylate-based, Mw 350,000, effective concentration 50% by mass) to the respective lubricant base oils of Examples 7 and 8 and Comparative Examples 6 to 8, respectively. The kinematic viscosities and the viscosity indexes of the respective lubricant oil compositions are shown in Table 2.

[JC08 Cold Mode Fuel Consumption Evaluation Test]

With respect to the lubricant oil compositions of Examples 9, 10, and Comparative Examples 9 to 11, a JC08 cold mode fuel consumption evaluation test was performed according to the following procedure.

JC08 mode is a method for measuring fuel consumption of vehicles, established by Ministry of Land Infrastructure, Transport and Tourism (for details, refer to Ministry of Land, Infrastructure, Transport and Tourism, Announcement that Prescribes Details of Safety Standards for Road Trucking Vehicles [2009.07.30] Attachment 42 Measurement Method of Exhaust Gas of Light and Middle Vehicles). JC08 is classified into a cold mode that starts in an engine cold state and a hot mode that measures fuel consumption in an engine warm state. In the test, a 2.5 L, FF gasoline engine vehicle (Toyota ESTIMA) was selected, the engine was washed and filled with a newly-prepared sample oil before the start of the test, the test vehicle was made to warm up at a constant rate of 60±2 km/h for 15 minutes or more on a chassis dynamometer, and then, was quickly returned to the idling state, the vehicle was driven one time in a predetermined running pattern, and then, was left (soak) in the stopped state in a room of 298±5K (25±5° C.) for 6 hours or more and 36 hours or less, and then, was driven in a predetermined pattern, and consumed fuel was calculated from driving exhaust gas to determine fuel consumption.

The obtained results are shown in Table 4.

[Storage Stability Test]

With respect to the sample oils of Examples 9, 10, and Comparative Examples 9 to 11, a storage stability test was performed according to the following procedure.

In a 100 ml screw vial, an oil is charged to two thirds or more thereof, and each of the test tube is put in a refrigerator of 0±1° C., and the appearance is confirmed after 48 hours. Without change in the appearance is evaluated as without change, and generation of condensation is evaluated as condensation.

The obtained results are shown in Table 4.

TABLE 4 Comparative Comparative Comparative Example 9 Example 10 Example 9 Example 10 Example 11 Base oil Kind Example 7 Example 8 Comparative Comparative Comparative Example 6 Example 7 Example 8 Content (% by mass) Balance Balance Balance Balance Balance Package additive 10 10 10 10 10 (% by mass) Viscosity index improver 5 5 5 5 5 (% by mass) Characteristics of compounded oil (5W-30) Kinematic viscosity, mm²/s (100° C.) 10.4 10.3 10.3 9.95 9.97 Viscosity index 255 250 252 245 238 JC08 cold mode fuel consumption 4.5 4.2 0.3 0.22 0.15 Rate of fuel consumption improvement, % Storage stability (0° C.) Without Without Condensation Condensation Condensation change change

Examples 11 to 13, Comparative Examples 12 to 14

In Examples 11 to 13 and Comparative Examples 12 to 14, lubricant base oils shown in Table 5 were each prepared. The lubricant base oils in Examples 11 to 13 are obtained based on the method for producing a lubricant base oil according to the above-described embodiment. In contrast, the lubricant base oils in Comparative Examples 12 to 14 are obtained by the conventional method for producing a lubricant base oil. Various characteristics of the respective base oils, and the traction coefficients measured under conditions of a load of 50 N (average hertz pressure 0.60 GPa), a sample oil temperature of 50° C., a circumferential velocity of 1 m/s, and a slip ratio of 3%, and using a 27.4 mm steel ball and a steel disc are shown in Table 1.

TABLE 5 Comparative Comparative Comparative Example 11 Example 12 Example 13 Example 12 Example 13 Example 14 General physical properties Density, g/cm³ 0.8054 0.8055 0.8056 0.8057 0.8058 — Flash point, ° C. 204 202 200 205 197 — Kinematic viscosity, mm²/s  (40° C.) 9.23 8.10 9.16 9.19 9.22 8.48 (100° C.) 2.70 2.45 2.66 2.70 2.65 2.51 Viscosity index 138 133 131 140 129 127 Pour point, ° C. −11 −22.5 −27.5 −7.5 −30 −40 Freezing point, ° C. −15 −24 −28 −8 −31 −43 NOACK, mass % (250° C.) 44.8 46.2 48.6 52.8 56.2 55.1 Sulfur content, mass ppm <10 <10 <10 <10 <10 <10 Iodine value 0.08 0.07 0.08 0.07 0.09 0.07 Aniline point, ° C. 111.1 110.6 110.7 112.5 111.8 112.0 Chromatography analysis Saturated content, mass % 99.6 99.4 99.5 99.6 99.6 99.3 Resin content, mass % 0.3 0.3 0.3 0.2 0.2 0.3 Aromatic content, mass % 0.1 0.3 0.2 0.2 0.2 0.4 Recovery rate, mass % 100 100 100 100 100 100 Urea adduct amount, mass % 9.68 4.25 4.02 12.5 0.58 0.11 nP, mass % 15.2 23.9 22.2 14.8 32.8 37.5 nP Base oil conversion amount, mass % 1.47 1.02 0.89 1.85 0.19 0.04 Raffinate physical properties Kinematic viscosity, mm²/s  (40° C.) 9.121 8.071 9.102 8.955 9.283 8.481 (100° C.) 2.675 2.451 2.639 2.651 2.629 2.498 Viscosity index 137 134 130 139 128 125 Pour point, ° C. −25 −42.5 −42.5 −20 −42.5 −45 Freezing point, ° C. −27 −43 −45 −22 −44 −46 ΔFreezing point (adduct-base oil) −16 −19 −17 −14 −13 −3 Low-temperature characteristics SBV viscosity, mP · s (−20° C.) 1,500 100 110 4,500 130 <1000 (−25° C.) 3,100 430 240 37,000 200 — (−30° C.) 19,200 2,120 1,050 49,000 780 270 (−35° C.) 290,000 13,300 3,300 900,000 1,970 1,040 (−40° C.) 720,000 29,000 5,300 >1,000,000 3,830 2,110 C13-NMR CH 7.6 7.8 7.7 7.4 7.7 7.6 CH2 76.4 76.1 75.9 76.6 76.0 75.6 CH3 16.0 16.1 16.2 16.0 16.3 16.8 CH2 main chain 16.9 16.4 15.1 17.1 13.3 10.1 EI-MS Paraffins 98.2 98.1 97.9 98.3 98.0 97.7 Monocyclic cycloparaffin 0.0 0.0 0.0 0.0 0.0 0.0 Bicyclic cycloparaffin 1.3 1.5 1.4 1.5 1.7 1.7 Tricyclic cycloparaffin 0.3 0.4 0.3 0.1 0.3 0.3 Tetracyclic cycloparaffin 0.1 0.0 0.2 0.0 0.0 0.0 Pentacyclic cycloparaffin 0.0 0.0 0.0 0.1 0.0 0.0 Hexacyclic cycloparaffin 0.1 0.0 0.2 0.0 0.0 0.3 Alkylbenzenes 0.0 0.0 0.0 0.0 0.0 0.0 FD-MS Paraffins 79.9 76.2 70.4 82.1 68.5 67.9 Monocyclic cycloparaffin 18.5 20.1 25.8 16.3 26.4 27.3 Bicyclic cycloparaffin 1.2 2.9 3.0 1.1 4.0 4.1 Tricyclic cycloparaffin 0.2 0.3 0.5 0.3 0.5 0.4 Tetracyclic cycloparaffin 0.0 0.0 0.0 0.0 0.0 0.0 Pentacyclic cycloparaffin 0.1 0.0 0.1 0.0 0.1 0.0 Hexacyclic cycloparaffin 0.1 0.5 0.2 0.2 0.5 0.3 Traction coefficient 0.013 0.014 0.015 0.011 0.016 0.019

Examples 14 to 16, Comparative Examples 15 to 17

Lubricant oil compositions were prepared by adding 8% by mass of a package additive (breakdown: antiwear agent: 12% by mass, ashless dispersant: 50% by mass, pour-point depressant: 1% by mass, antioxidant: 12% by mass, detergent: 25% by mass) and 5% by mass of a viscosity index improver (polymethacrylate-based, Mw 350,000, effective concentration 50%) to the respective lubricant base oils. The SBV viscosities of the respective lubricant oil compositions at −40° C. are shown in Table 6.

[SRV Friction Test]

With respect to the lubricant oil compositions of Examples 14 to 16, and Comparative Examples 15 to 17, an SRV friction test was performed using an SRV friction tester at a temperature of −30° C., a load of 50 N, a frequency of 10 Hz, and an amplitude of 1 mm, and a friction coefficient was measured. The obtained results are shown in Table 6.

TABLE 6 Comparative Comparative Comparative Example 14 Example 15 Example 16 Example 15 Example 16 Example 17 Base oil Kind Example 11 Example 12 Example 13 Comparative Comparative Comparative Example 12 Example 13 Example 14 Content (% by Balance Balance Balance Balance Balance mass) Package additive (% by 8 8 8 8 8 8 mass) Viscosity index 5 5 5 5 5 5 improver (% by mass) Characteristics of 340,000 16,000 5,800 >1,000,000 4,020 2,600 compounded oil SBV viscosity, mPa · s (−40° C.) SRV friction test 0.108 0.121 0.128 Friction 0.155 0.165 Friction coefficient coefficient abnormal 

1. A lubricant base oil that is a hydrocarbon oil having a kinematic viscosity at 100° C. of 2.0 to 9 mm²/s, a viscosity index of 130 or more, a freezing point of −30 to −5° C., and an SBV viscosity at −20° C. of 1,000 to 60,000 mPa·s, wherein the freezing point of the lubricant base oil is higher by 10° C. or more than a freezing point of raffinate obtained by bringing the lubricant base oil into contact with urea and removing paraffin that can be included in the urea.
 2. The lubricant base oil according to claim 1, which is a hydrocarbon oil having a kinematic viscosity at 100° C. of 3.0 to 5.0 mm²/s, a viscosity index of 145 or more, a freezing point of −20 to −5° C., and an SBV viscosity at −20° C. of 3,000 to 60,000 mPa·s, wherein the freezing point of the lubricant base oil is higher by 10° C. or more than a freezing point of raffinate obtained by bringing the lubricant base oil into contact with urea and removing paraffin that can be included in the urea.
 3. The lubricant base oil according to claim 1, which is a hydrocarbon oil having a kinematic viscosity at 100° C. of 5 to 9 mm²/s, a viscosity index of 155 or more, a freezing point of −15 to −5° C., and an SBV viscosity at −20° C. of 3,000 to 30,000 mPa·s, wherein the freezing point of the lubricant base oil is higher by 10° C. or more than a freezing point of raffinate obtained by bringing the lubricant base oil into contact with urea and removing paraffin that can be included in the urea.
 4. The lubricant base oil according to claim 1, which is a hydrocarbon oil having a kinematic viscosity at 100° C. of 2.0 to 3.0 mm²/s, a viscosity index of 130 or more, a freezing point of −30 to −10° C., and an SBV viscosity at −30° C. of 1,000 to 30,000 mPa·s, wherein the freezing point of the lubricant base oil is higher by 15° C. or more than a freezing point of raffinate obtained by bringing the lubricant base oil into contact with urea and removing paraffin that can be included in the urea.
 5. A method for producing a lubricant base oil, the method comprising: a first step of fractionating, from a hydrocarbon oil containing a base oil fraction and a heavy fraction that is heavier than the base oil fraction, the base oil fraction and the heavy fraction; a second step of returning a cracked oil obtained by hydrocracking the heavy fraction fractionated in the first step, to the first step; a third step of obtaining a dewaxed oil by performing hydroisomerization dewaxing of the base oil fraction; a fourth step of obtaining a refined oil by refining the dewaxed oil; and a fifth step of obtaining a lubricant base oil that is a hydrocarbon oil having a kinematic viscosity at 100° C. of 2.0 to 9 mm²/s, a viscosity index of 130 or more, a freezing point of −30 to −5° C., and an SBV viscosity at −20° C. of 1,000 to 60,000 mPa·s, by fractionation of the refined oil, wherein the third step is a step of performing hydroisomerization dewaxing of the base oil fraction such that the freezing point of the lubricant base oil obtained in the fifth step is higher by 10° C. or more than a freezing point of raffinate obtained by bringing the lubricant base oil into contact with urea and removing paraffin that can be included in the urea.
 6. The method according to claim 5, wherein the fifth step is a step of obtaining a lubricant base oil that is a hydrocarbon oil having a kinematic viscosity at 100° C. of 3.0 to 5.0 mm²/s, a viscosity index of 145 or more, a freezing point of −20 to −5° C., and an SBV viscosity at −20° C. of 3,000 to 60,000 mPa·s, by fractionation of the refined oil, and the third step is a step of performing hydroisomerization dewaxing of the base oil fraction such that the freezing point of the lubricant base oil obtained in the fifth step is higher by 10° C. or more than a freezing point of raffinate obtained by bringing the lubricant base oil into contact with urea and removing paraffin that can be included in the urea.
 7. The method according to claim 5, wherein the fifth step is a step of obtaining a lubricant base oil that is a hydrocarbon oil having a kinematic viscosity at 100° C. of 5 to 9 mm²/s, a viscosity index of 155 or more, a freezing point of −15 to −5° C., and an SBV viscosity at −20° C. of 3,000 to 30,000 mPa·s, by fractionation of the refined oil.
 8. The method according to claim 5, wherein the fifth step is a step of obtaining a lubricant base oil that is a hydrocarbon oil having a kinematic viscosity at 100° C. of 2.0 to 3.0 mm²/s, a viscosity index of 130 or more, a freezing point of −20 to −5° C., and an SBV viscosity at −30° C. of 1,000 to 30,000 mPa·s, by fractionation of the refined oil, and the third step is a step of performing hydroisomerization dewaxing of the base oil fraction such that the freezing point of the lubricant base oil obtained in the fifth step is higher by 15° C. or more than a freezing point of raffinate obtained by bringing the lubricant base oil into contact with urea and removing paraffin that can be included in the urea.
 9. The method according to claim 5, wherein the third step is a step of performing hydroisomerization dewaxing of the base oil fraction in the presence of a hydroisomerization catalyst containing at least one crystalline solid acidic substance selected from the group consisting of ZSM-22-type zeolite, ZSM-23-type zeolite, SSZ-32-type zeolite, and ZSM-48-type zeolite, and platinum and/or palladium as an active metal.
 10. The method according to claim 5, wherein the hydrocarbon oil in the first step is obtained by using GTL wax obtained by a Fischer-Tropsch synthesis or slack wax obtained by solvent dewaxing, as a raw material. 